How Much Does Water Weigh? Exact Weights Guide

Water is not only essential because of its physical properties like density and weight — it’s also a fundamental resource for life and public health. Safe, readily available drinking water is critical for health, domestic use, food production, and economic development, according to the World Health Organization. How heavy is water depends on its volume, the temperature of the water, and what is dissolved in it. Under standard conditions near 4 °C (39 °F), 1 liter of pure water weighs about 1 kilogram, or roughly 2.205 pounds, and 1 U.S. gallon of water weighs about 8.34 pounds (3.78 kg). In this guide you’ll get clear numbers, a simple calculation method, and real‑world examples so you can work out the exact weight of almost any amount of water.

Quick Answer: How Much Does Water Weigh?

To put it simply, 1 liter of pure water weighs about 1 kilogram (2.205 lb) at about 4 °C, and 1 U.S. gallon of water weighs about 8.34 lb (3.78 kg) at around 4–20 °C.

Because water density is close to 1 at these temperatures, several handy rules follow:

1 milliliter (mL) of water weighs about 1 gram (g).
1000 mL = 1 liter (L), and 1 liter of water weighs close to 1000 grams, or 1 kg.
1 cubic meter (m³) of water contains 1000 L and weighs about 1000 kg, which is 1 metric ton.

The mass of water (in kilograms or grams) stays the same, but its weight (in pounds or newtons) can change slightly with temperature, impurities like salt, and local gravity. For home, cooking, and most building uses, the numbers above are accurate enough.

Water Weight Chart: Liters, Gallons, Cups & More

Most people come to this question because they want a number they can use right away. Maybe you are filling a tank, moving a 5‑gallon jug, checking floor load, or converting liters of drinking water into pounds for a hike. Instead of doing the math from scratch every time, you can use a few standard conversions.

At about 4–20 °C (39–68 °F), fresh water has a density close to 1 g/mL (or 1 kg/L). That means water weight scales almost one‑to‑one with volume in metric units. In U.S. units, 1 U.S. gallon of water weighs about 8.34 pounds, so you can scale from that.

Basic Metric Conversions (mL, L, m³)

Detailed tabulated values for water density and specific weight at different temperatures and units (kg/m³, lb/gal) are available on Engineering Toolbox’s reference page, which can be used to refine weight calculations beyond the simple 1 kg per liter rule.

1 mL of water weighs about 1 g.
100 mL weighs about 100 g (0.1 kg).
250 mL (a small glass) weighs about 250 g (0.25 kg, or about 0.55 lb).
500 mL (a typical bottle) weighs about 500 g (0.5 kg, or about 1.1 lb).
The weight of one liter of water is about 1 kg (2.205 lb).
10 L weighs about 10 kg (22.05 lb).
1 m³ of water (1000 L) weighs about 1000 kg, or 1 metric ton (about 2205 lb).

If you remember that 1 mL ≈ 1 g, 1 L ≈ 1 kg, and 1 m³ ≈ 1 ton, you can handle most metric water weight questions in your head.

U.S. Cooking & Household Measures

When you move to cups, pints, and gallons, the numbers are not as tidy, but they are still simple once you know a few key values. At room temperature:

1 U.S. cup of water (about 240 mL) weighs about 0.52 lb (0.237 kg).
1 U.S. pint (2 cups, about 473 mL) weighs about 1.04 lb (0.473 kg).
1 U.S. quart (2 pints, about 946 mL) weighs about 2.09 lb (0.946 kg).
1 U.S. gallon (3.785 L) weighs about 8.34 lb (3.78 kg).

So if you ever ask “how much does a gallon of water weigh?” the weight of a gallon of water for most everyday uses is about 8.34 pounds for a U.S. gallon.

This leads to a related question: Does 16 oz of water weigh 1 lb? In U.S. units, 16 ounces by weight always equals 1 pound by definition. But 16 fluid ounces is a measure of volume, not weight. A 16‑fl‑oz glass of water actually weighs closer to 16.7 ounces (about 1.04 lb), because 1 U.S. fluid ounce of water weighs about 1.043 ounces. So people are close when they say “16 oz of water is a pound,” but the true value is a bit more than 1 lb.

Common Larger Volumes

As volume grows, water gets heavy very quickly. Here are some numbers many people need for work, building projects, or water storage:

5 U.S. gallons of water (large jug) is about 18.9 L and weighs about 41.7 lb (18.9 kg).
10 U.S. gallons is about 37.9 L and weighs about 83.4 lb (37.9 kg).
A 55‑gallon drum filled with water holds about 208 L and weighs about 458 lb (208 kg) just for the water.
1 cubic foot of water weighs about 62.4 lb (28.3 kg).

So if you are planning to store several drums of water in a shed, or install a large aquarium or water filtration tank, it is smart to add up these weights and compare them to what the floor can safely support.

U.S. vs Imperial (UK) Gallons

Another common source of confusion is that not all gallons are the same size. A U.S. gallon is smaller than an Imperial (UK) gallon.

1 U.S. gallon ≈ 3.785 L and weighs about 8.34 lb at room temperature.
1 Imperial gallon ≈ 4.546 L, and at about 4 °C an Imperial gallon of water weighs about 10.02 lb (4.54 kg).

So if you are converting gallons to weight, always check whether someone is using U.S. gallons or Imperial gallons.

Consolidated Water Weight Conversion Table

The table below shows the approximate weight of water at about 4–20 °C (39–68 °F), for fresh water at normal atmospheric pressure.

Volume / Measure	Approx. Volume (L)	Metric weight (kg)	Weight (lb)
1 milliliter (mL)	0.001	0.001	0.0022
100 mL	0.1	0.1	0.22
250 mL (small glass)	0.25	0.25	0.55
500 mL (bottle)	0.5	0.5	1.1
1 liter (L)	1	1	2.205
10 liters	10	10	22.05
1 cubic meter (m³)	1000	1000	2205
1 U.S. cup (~240 mL)	0.237	0.237	0.52
1 U.S. pint (2 cups)	0.473	0.473	1.04
1 U.S. quart (2 pints)	0.946	0.946	2.09
1 U.S. gallon	3.785	3.78	8.34
5 U.S. gallons	18.9	18.9	41.7
10 U.S. gallons	37.9	37.9	83.4
55 U.S. gallons (drum)	208	208	458
1 cubic foot	28.3	28.3	62.4
1 Imperial (UK) gallon	4.546	4.54	10.02

These values give you a fast way to convert between milliliters, liters, gallons, and pounds without doing a full calculation.

Water Weight Calculator (By Volume and Temperature)

If you need more than rough figures, you can calculate the weight of water using a simple formula. Any water weight calculator, whether online or on a spreadsheet, usually does the same thing behind the scenes.

To calculate how heavy water is, you need:

The volume of water (in mL, L, U.S. gallons, Imperial gallons, cups, pints, quarts, or cubic feet).
The temperature of the water in °C or °F.
The type of water (fresh water, seawater, or ice), because density changes with salt and with solid vs liquid.

A calculator then works like this:

It converts your volume into liters or cubic meters.
It looks up or computes the density of water at that temperature. For example, at 20 °C the density of fresh water is about 0.998 g/mL, not a perfect 1.000.
It uses the standard formula:

Mass of water = Density × Volume

Weight of water = Mass × local gravity

On Earth at sea level, gravity is about 9.81 m/s², so most tools simply fold that into the density and give you the answer straight in kilograms or pounds.

This “water weight calculator” idea is often what people mean when they search for water weight per gallon, weight of water calculator, or water density converter. You can also build your own calculator in a spreadsheet using density values from an official table.

What Determines How Much Water Weighs? (Density Explained)

To understand why water weighs what it does, and why the weight changes slightly, you need to know a bit about density.

Density 101

Density tells you how much mass fits in a certain volume. The basic formula is:

Density = Mass ÷ Volume

We usually measure water density in grams per milliliter (g/mL), kilograms per liter (kg/L), or kilograms per cubic meter (kg/m³).

For liquid water close to 4 °C (39 °F):

Density ≈ 1.000 g/mL
Which is the same as 1 kg/L
And 1000 kg/m³

Because of this, we can say:

1 mL of water weighs about 1 gram.
1 L of water weighs about 1 kilogram.
1 m³ of water weighs about 1000 kilograms.

You may also see decimals like 0.998 g/mL at 20 °C. That value shows water becomes slightly less dense as it warms up. The key point is that near room temperature, density is close to 1, which makes metric water conversions very simple.

Mass vs Weight

People also mix up mass and weight. They are related but not the same.

Mass measures how much matter something has. It is measured in grams (g) or kilograms (kg) and stays the same everywhere.
Weight measures how strongly gravity pulls on that mass. It is measured in newtons, or in pounds (lb) in daily life, and it changes with gravity.

So 1 liter of water has a mass of about 1 kg wherever you take it, but it will weigh less on the Moon and weigh more on a high‑gravity planet. On Earth, at normal conditions, we often talk loosely and say “a liter weighs 1 kilogram,” but what we mean is that its mass is 1 kg and its weight matches that under Earth gravity.

The Core Formula

Once you know density, you can find how much water weighs with two steps:

Mass = Density × Volume
Weight = Mass × Local Gravity

Here is a quick example. Imagine you have 3 L of water at about 20 °C. At that temperature, the density is about 0.998 kg/L.

Mass = 0.998 kg/L × 3 L = 2.994 kg.
To convert that mass to pounds, multiply by 2.20462: 2.994 kg × 2.20462 ≈ 6.6 lb.

So 3 L of room‑temperature water weighs about 6.6 pounds.

How Temperature Changes the Weight of a Gallon or Liter

You may have heard that water is densest at about 4 °C (39 °F). That is correct, and it matters when you want precise numbers, such as in engineering, science experiments, or careful building plans.

Why Water Is Heaviest at 4 °C (39 °F)

Most substances just shrink as they cool and expand as they warm. Water is special. Its water molecules arrange themselves in a way that makes liquid water reach its highest density around 4 °C. That means at 4 °C:

1 L of water weighs almost exactly 1.000 kg.
1 U.S. gallon of water weighs about 8.345 lb.
1 Imperial gallon of water weighs about 10.02 lb.

If water is colder than 4 °C but still liquid, or warmer than 4 °C, the molecules are slightly farther apart. The water becomes less dense, so the same volume weighs slightly less.

Temperature–Density–Weight Table

Here is a compact table that shows how water density and weight shift with temperature for fresh water at normal atmospheric pressure. The weights for a liter and a U.S. gallon follow directly from the density.

Temperature (°C / °F)	Approx. Density (g/mL)	1 liter (kg)	1 U.S. gallon (lb)
0 °C / 32 °F	0.9998	0.9998	~8.344
4 °C / 39 °F	1	1	~8.345
20 °C / 68 °F	0.998	0.998	~8.33
25 °C / 77 °F	0.997	0.997	~8.32
100 °C / 212 °F	0.958	0.958	~8.0

You can see that water at 20–25 °C is slightly less dense than at 4 °C. That is why we often say “1 liter of water weighs 1 kg” as a rule of thumb, even though at room temperature it is closer to 0.998 kg.

This also answers another common question: Does warm water weigh less than cold water? For the same volume, yes. As water warms, its density decreases. So a gallon of warm water weighs slightly less than a gallon of cold water.

Freshwater vs Saltwater vs Ice: Which Weighs More?

Now that you know temperature affects water density, you might wonder about salt, or even ice. Does salty water weigh more? Does ice weigh less?

Freshwater (Baseline)

When we talk about “standard” water weight, we usually mean fresh water with very little dissolved material. At about 4 °C, fresh water has its highest density, very close to 1.000 g/mL. That is the basis for the rule that 1 liter of water weighs 1 kilogram.

Everyday tap water is quite similar, though tiny amounts of dissolved minerals may change the density by a very small amount. For home use, we usually treat tap water as if it has the same density as pure fresh water.

Saltwater (Seawater)

Saltwater is heavier per unit volume because it contains dissolved salts and other substances. Typical seawater has a density around 1.025 g/mL, though it can vary with salinity and temperature.

This means:

Seawater is about 2.5% more dense than freshwater.
1 L of seawater weighs about 1.025 kg.
1 U.S. gallon of seawater weighs about 8.55 lb.

This higher density is why people float more easily in the ocean than in a lake. It also matters a lot in ocean research, ship design, and saltwater aquariums, where small changes in salinity and temperature affect how things float or sink.

Ice vs Liquid Water

Ice is the same water in a different form, but it is less dense. At 0 °C, typical ice has a density of about 0.917 g/mL.

So:

1 L of ice has a mass of about 0.917 kg.
That is about 9% lighter than the same volume of cold liquid water.

This is why ice floats in liquid water. The ice takes up more space for the same mass of water, so it is less dense and sits on the surface. If you filled a container completely with water, then froze it, the volume would expand and the ice would push against the sides.

Gravity, Altitude, and Location: Do They Change Water’s Weight?

So far, we have assumed normal Earth gravity at sea level. But gravity is not exactly the same everywhere.

Gravity and Weight

Remember that:

The mass of water (in kg) stays the same whether you are on Earth, on a mountain, or on the Moon.
Weight (in lb or newtons) depends on local gravity.

On Earth, gravity is a little stronger near the poles and a bit weaker near the equator. It also gets slightly weaker as you move higher in altitude. This means:

A liter of water will weigh very slightly less in the mountains than at sea level.
The change is tiny for daily life, usually less than 1%.

For most home, cooking, plumbing, or construction work, you can ignore these small changes in gravity and keep using the standard values. If you work in very precise science or engineering fields, you may adjust water weight based on the exact location.

As a thought experiment, imagine a 1 U.S. gallon jug of water. Its mass is always about 3.78 kg. On a high‑gravity planet it might weigh much more, and on the Moon it would weigh much less, even though the number of water molecules stays the same.

Real‑World Examples of Water Weight

Knowing the weight of water is not just a science exercise. It affects many daily tasks: lifting containers, planning storage, building pools or tanks, and even planning how much drinking water to carry.

How Much Does a 5‑Gallon Water Jug Weigh?

If you have ever tried to lift a full 5‑gallon water jug onto a cooler, you know how heavy water can feel. Let’s do the math.

A 5‑gallon jug holds about 18.9 L of water.
Each liter has a mass of about 1 kg.
So the jug holds about 18.9 kg of water.

To convert kilograms to pounds, multiply by 2.20462:

18.9 kg × 2.20462 ≈ 41.7 lb.

So the weight of 5 gallons of water is about 41.7 pounds. When you add the plastic jug itself, the total is a bit more. This is why safe lifting and good back posture matter when you move several jugs at once.

This also links back to one of the key questions: Which is heavier, 5 gallons of water or 5 gallons of sand? 5 gallons of sand is heavier. Sand is more dense than water. Depending on the type of sand, 5 gallons can weigh around 60–70 lb or more, which is much heavier than 5 gallons of water at about 41.7 lb.

How Much Does the Water in a Swimming Pool Weigh?

Imagine a small in‑ground pool that is 10 m long, 4 m wide, and 1.5 m deep on average. Its volume is:

10 m × 4 m × 1.5 m = 60 m³.

Each cubic meter of water holds 1000 L and has a mass of about 1000 kg. So:

60 m³ of water holds about 60,000 L.
Mass ≈ 60,000 kg, which is 60 metric tons.
In pounds, that is about 132,000 lb.

This huge water weight is why pool walls, floors, and nearby buildings must be carefully designed. Builders and engineers consider water volume, water density, and safety factors so the structure holds up over many years.

Water in Tanks, Barrels, and Totes

Water storage is common on farms, in factories, and in emergency planning. Knowing how heavy water is helps you size supports and choose safe locations. When dealing with large amounts of stored water, knowing the weight is only part of the picture. Many homeowners also use a smart water monitor to track water usage, detect leaks, and better manage how much water is moving through their system over time.

A 55‑gallon drum full of water weighs about 458 lb (208 kg) of water, plus the drum.
A 275‑gallon tote holds about 1041 L and the water alone weighs around 2290 lb (about 1040 kg).
A 330‑gallon tote holds about 1250 L and the water inside weighs around 2750 lb (about 1250 kg).

If you place these on a wooden floor or a truck bed, that weight is concentrated in a small area. Floor load ratings (in lb/ft² or kg/m²) tell you how much weight is safe. Since water is one of the heaviest everyday liquids by volume, a small mistake in planning can lead to damage.

The same idea applies to large home water heaters, big aquariums, and whole‑house water filtration tanks. A 75‑gallon tank, for example, holds over 625 lb of water.

Daily Drinking Water and “Water Weight”

Think about your daily drinking water. Many health guides suggest around 2 L of total fluids per day for many adults, depending on climate, food, and activity. If someone drinks about 2 L of plain water:

That is about 2 kg of water.
In pounds, 2 kg is about 4.4 lb.

Of course, this water does not just “sit” in your body. Your body uses it and removes it, so your body mass from water remains fairly balanced if intake and loss match. When people talk about “water weight” in dieting, they often mean short‑term changes in how much water the body holds in tissues, not permanent gains in mass.

Why 1 Liter of Water ≈ 1 Kilogram (History & Science)

The neat link between volume of water and mass of water is not an accident. It comes from how the metric system was built.

When scientists first set up the metric system, they wanted units that were simple and connected. They defined the kilogram in terms of water:

1 kilogram was set as the mass of 1 liter of pure water at 4 °C, at standard atmospheric pressure.

Because water is densest at 4 °C, this gave them a stable reference. Later, the official definition of the kilogram changed. Today, it is defined using physical constants measured in very fine experiments, not by a piece of metal or a certain amount of water.

Even so, the old link remains very useful in daily life. You can keep using:

“1 liter of water weighs approximately 1 kilogram.”
“1 mL of water weighs approximately 1 gram.”

You only need more precise values if you are doing careful lab work, high‑level engineering, or very large‑scale water planning where a 1–2% error might matter.

To answer a common question directly: Does 1 litre of water weigh 1 kg? Under standard conditions near 4 °C, yes, 1 liter of water weighs 1 kilogram. At typical room temperature, it weighs slightly less, about 0.998 kg, but for most needs, saying “1 liter of water weighs 1 kg” is fine.

And if you wonder how much a liter of water weighs in pounds, the answer is about 2.205 lb (since 1 kg ≈ 2.20462 lb).

Summary: Key Numbers to Remember About Water Weight

To put the main points in one place:

1 mL of water weighs about 1 gram (1 g).
1 L of water weighs about 1 kilogram (1 kg), or 2.205 lb, at around 4 °C.
1 U.S. gallon of water weighs about 8.34 lb (3.78 kg) near room temperature.
5 U.S. gallons of water weigh about 41.7 lb (18.9 kg).
An Imperial gallon is larger and weighs about 10.02 lb (4.54 kg) at 4 °C.

Temperature, dissolved salts, and local gravity can make water weigh slightly less or slightly more for the same volume, but for most home, cooking, and building uses you can rely on these simple rules. When you need more exact values — for large tanks, pools, or careful engineering — you can use water density tables and a calculator to match the temperature of water and the volume of water to its mass and weight.

Knowing how much water weighs, by liter, gallon, cup, or cubic foot, helps you cook, carry, store, and build with water safely and confidently.

FAQs

1. What does 1 gallon of water weigh?

That depends on which gallon you’re talking about. In the United States, 1 U.S. gallon of water weighs about 8.34 pounds (or 3.78 kilograms) at room temperature. This is the number most people in the U.S. use for everyday reference. In the UK and some other countries, an Imperial gallon is larger. An Imperial gallon of water weighs about 10.02 pounds (around 4.54 kilograms) at about 4 °C. So if you ever see different numbers for a “gallon of water,” it’s usually because different gallon systems are being used.

2. How much does a litre of water weight in pounds?

A litre of water weighs about 1 kilogram, and since 1 kilogram equals roughly 2.20462 pounds, a litre of water comes out to about 2.2 pounds. This is a really handy conversion to remember because it’s so clean and consistent. Unless you’re doing high-precision scientific work, rounding to 2.2 pounds is more than accurate enough for daily use.

3. Does 16 oz of water weigh 1 lb?

This one can be a bit confusing because “ounces” can mean two different things. If you’re talking about 16 ounces by weight, then yes—by definition, that equals exactly 1 pound. However, if you mean 16 fluid ounces of water (which is a volume, not a weight), it actually weighs a bit more. Sixteen fluid ounces of water weigh about 16.7 ounces, or roughly 1.04 pounds. So it’s close, but not exactly the same.

4. Which is heavier, 5 gallons of water or 5 gallons of sand?

Five gallons of water weigh about 41.7 pounds. Sand, on the other hand, is much denser than water. Depending on the type of sand and how dry or compact it is, 5 gallons of sand can easily weigh 60–70 pounds or even more. Because of that higher density, 5 gallons of sand are definitely heavier than 5 gallons of water, even though the volume is the same.

References

https://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

https://www.who.int/news-room/fact-sheets/detail/drinking-water