How many kilos in 1 liter?

As an SEO writer, let’s start this article by quickly answering the question posed in the title – how many kilos are in 1 liter? The quick answer is that 1 liter of water equals 1 kilogram. This is because, by definition, 1 kilogram is the mass of 1 liter of water at 4°C. So 1 liter of water at 4°C equals exactly 1 kilogram. This provides a simple way to convert between liters and kilograms.

The Liter as a Unit of Volume

To fully answer the question of how many kilos are in 1 liter, we first need to understand what a liter is measuring. A liter is a unit of volume, commonly used to measure the volumes of liquids. Specifically, a liter is defined as 1 cubic decimeter. A decimeter is one tenth of a meter. So a liter is the volume occupied by a cube that measures 10 centimeters on each side.

The liter is a unit that is commonly used to measure volumes of liquids in cooking, mixing drinks, measuring fuel consumption of vehicles, quantifying the capacity of containers, and in many other everyday applications. For example, a typical bottle of soda contains 2 liters. When following a recipe, you may be instructed to add 250 milliliters (ml) of milk, where 1000 ml equals 1 liter.

Origins and History of the Liter

The liter was originally introduced as part of the metric system in France during the French Revolution. The metric system was created to establish a uniform set of measurements across Europe. The liter was defined as 1 cubic decimeter of water. The metric system quickly spread and is now used in most countries around the world. The liter is a practical unit for measuring everyday volumes and remains in common use today.

The Kilogram as a Unit of Mass

Now that we understand what a liter measures, we need to understand what a kilogram measures. While a liter is a unit of volume, a kilogram is a unit of mass. Specifically, a kilogram is defined as the mass of the International Prototype Kilogram. This cylinder of platinum-iridium alloy is precisely machined to weigh the equivalent of 1 liter of water at 4°C.

So while a liter measures the volume occupied by a cube of water, a kilogram measures its mass. The mass of 1 liter of water at 4°C was chosen as the definition of 1 kilogram because water has a density of 1 g/cm3 at that temperature. This makes calculating volumes and masses easy.

The kilogram is the primary unit of mass in the metric system. It is used to measure the mass of objects ranging from the amount of flour in a recipe to the payload of a rocket. Like the liter, it was introduced during the French Revolution and later standardized across the metric system.

International Prototype Kilogram

The original definition of the kilogram was based on a physical cylinder of platinum-iridium alloy known as the International Prototype Kilogram or IPK. This was precisely machined in the 1880s to have the mass of 1 liter of water under specified conditions. The IPK cylinder was stored under controlled conditions at the International Bureau of Weights and Measures near Paris.

Replicas of the IPK were distributed around the world to define the kilogram in different countries. However, over time, the IPK and its replicas were found to drift slightly in mass relative to one another. This led to a new definition of the kilogram taking effect in 2019 based on fundamental physical constants.

The Density of Water

We’ve seen that a liter was originally defined as the volume occupied by 1 kilogram of water at 4°C. The reason this volume and temperature were chosen is because water has a density extremely close to 1 g/cm3 at 4°C. Specifically, at this temperature, one cubic centimeter of water has a mass of 0.999972 g. Rounded, this is essentially equal to 1 g/cm3.

This property makes water useful for defining units of mass and volume. The density of liquid water at 4°C and 1 atm of pressure is:

Density SI Units
0.999972 g/cm3 or 1.000028 kg/L

The density varies slightly based on factors like temperature, pressure, and purity. But at 4°C and standard pressure, it is extremely close to 1 g/cm3. This allows the mass of a volume of water to be used to define the kilogram.

Anomalous Properties of Water

Water has many unique physical and chemical properties. One that is relevant when defining units of mass and volume is that water is most dense at 4°C, unlike most liquids. The maximum density at 4°C causes bodies of water to freeze from the top down, enabling aquatic life to survive underneath ice.

Water also has a high specific heat capacity, requiring substantial energy to change its temperature. Combined with the density maximum at 4°C, this helps moderate seasonal temperature changes in the oceans and provides stability to the climate.

So in summary, the anomalous physical properties of water at 4°C lend themselves well to defining standards of mass and volume.

Converting Between Liters and Kilograms

Now that we understand the units involved, converting between liters and kilograms is straightforward:

1 liter of water at 4°C equals:

  • 1 kilogram
  • 1000 grams
  • 0.001 cubic meters

And reversing the conversion:

1 kilogram equals:

  • 1 liter of water at 4°C
  • 1000 ml of water at 4°C

Some example conversions:

Liters Kilograms
2 liters 2 kg
0.5 liters 0.5 kg
2500 ml 2.5 kg

So 1 liter of water at 4°C equals 1 kilogram. This equivalence facilitates easy conversions between units of volume and mass.

Metric Conversions

The liter and kilogram are part of the metric system which is designed to allow easy conversions between units. Some other metric conversions include:

  • 1000 grams (g) = 1 kilogram (kg)
  • 1000 milliliters (ml) = 1 liter (L)
  • 100 centimeters (cm) = 1 meter (m)

So converting between units like grams and kilograms, or milliliters and liters is straightforward. The simplicity of the metric system makes it popular worldwide.

When the Equivalence Does Not Hold

It’s important to keep in mind that the equivalence of 1 liter and 1 kilogram is only exactly true for pure water at 4°C. For other substances, or water at different temperatures, the density will be different.

For example, at room temperature (25°C) the density of water is 0.997 g/ml. So 1 liter of water at room temperature would have a mass of 0.997 kg rather than 1 kg. For many everyday purposes this difference is negligible, but for scientific work it matters.

For other liquids like oil, alcohol, or honey, the density can differ significantly from 1 g/ml. So 1 liter of these substances would not equal 1 kilogram.

The equivalence also does not hold for gases. One liter of air at sea level contains roughly 1.2 grams of air. So a liter of air has a mass of 0.0012 kg, far less than 1 kg.

However, the 1 liter = 1 kg relationship remains valid for pure water at 4°C. And for many practical purposes with water and other liquids at everyday temperatures, the equivalence is a useful approximation.

Accounting for Temperature and Impurities

When accuracy is important, the conversion between liters and kilograms should account for the temperature and purity of the water.

For example, the density of water over a range of temperatures is:

Temperature (°C) Density (g/ml)
0 0.99984
10 0.99970
20 0.99820
30 0.99565

Salt, minerals, or other impurities also slightly alter the density. So for scientific work involving the mass and volume of water, these factors need to be considered.

Practical Examples

Let’s look at some practical examples of converting between liters and kilograms:


Many recipes involve converting between volume and mass units. For example, a recipe may call for 250g of flour. Since 1 kg of flour equals about 1 liter in volume, 250g would be about 0.25 liters.

When measuring liquids like water, milk, or oil at room temperature, the equivalence is approximate. For example 250 ml is approximately 0.25 kg.


Food packaging often lists both weight and volume. A 500g package of pasta may also list the volume as 500 ml. This allows convenient use of either units in recipes or comparisons between brands. Again, the equivalence holds exactly only for water at 4°C but provides a good approximation for many common foods.


When shipping containers of liquids like fuel, oil, or chemicals, product weight is calculated from the volume and density. Accurate product weight is needed to calculate shipping costs. Whether billing is based on weight or volume, the conversion allows different units to be interchanged.


In summary, 1 liter of pure water at 4°C is defined as having a mass of 1 kilogram. So under these specific conditions, liters and kilograms are equivalent units. This facilitates conversions between units of volume and mass.

For water at everyday temperatures, the equivalence holds closely enough for most practical purposes. But the conversion is not exact for other liquids or gases. Scientific work requires accounting for substance density and conditions like temperature and purity.

Still, knowing that 1 liter of water equals 1 kilogram provides a handy reference point. The relationship simplifies conversions involved in cooking, packaging, shipping, and any application involving volumes of water or similar liquids.

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