Does 1 litre of water weigh 1 kg?

Not true because a kilogram is a measure of mass - NOT of weight. The mass of one litre of water is approx 1 kilogram and ON THE SURFACE OF THE EARTH it would weigh around 9.8 Newtons. On the surface of the moon, it would weight around 1.6 Newtons and in outer space it would be weightless.

Besides, the density of water, at 1 atmosphere has a maximum value of 999.9720 kg/metre3 - near enough, but not quite 1,000.

As we know that a solid object has a fixed size and a fixed volume. Therefore, in a normal routine, we express the amount of a solid object in its mass. Such as 5 kg sugar, 10 kg flour, 2 kg rice etc.

But the fluid does not have a fixed shape. Although there is a definite volume. Therefore, as we place the fluid in the vessel, it takes its shape. So we measure amount of the fluid on the basis of its volume. Such as 2 liters of milk, 5 liters of water, 2 liters of petrol etc.

Now the question arises what happens if the fluid is also measured as mass. You will be surprised that the volume and mass of all liquids are not the same.

Illustrations-

Example-1 One litre of ice cream is equal to 540 gram.

Example 2 -One litre of ghee is not equal to 1 kg of ghee. 1 Litre ghee is equal to 905 gram.

Example 3 -One litre of Cooking Oil is equal to 910 gram.

General Perception

People generally think that 1 kg of liquid is equal to 1 litre of liquid. When we go to the market, we ask the shopkeeper to give 1 kg of ghee but he gives 1 litre of ghee. Why so?

This confusion arises for business benefits. Because only 905 grams of ghee comes in 1 liter of ghee, but the price is taken equal to 1 kg of ghee, similarly the same happens in other substances. Because the layman man knows that 1 kg of water is equal to 1 liter of water, which is also scientifically correct.

Let us now know why this happens?

In the language of science, the density of every object is equal to its mass divided by the volume . While the density of the fluid is less than solids. Difference in the density occurs due to different mass and volume ratio. The mass of objects may equal or greater or lesser than its volume . Density shows the packing of mass in the volume. If less mass of one substance in comparison of another substance is packed in a particular volume then its density will be less than given object and vice versa.

Litre v/s Kilogram

In the metric system of SI( International System) units, liters and kilograms are both important units of measurement of any substance. A litre is a unit of volume, or space while a kilogram is a unit of mass, representing a given quantity of matter.

In 1901, the General Conference on Weights and Measures defined 1 liter as the volume of exactly 1 kilogram of water at room temperature. i.e. the litre is defined in terms of kilogram in 1795.

The conversion from liters to kilograms would therefore be very simple if all substances were identical to water. Instead, liquids vary in their density, or the amount of mass per unit volume.

The SI unit of volume is the cubic meter (m 3 ), which is the volume occupied by a cube that measures 1 m on each side. This very large volume is not very convenient for typical use in a chemistry laboratory. A liter (L) is the volume of a cube that measures 10 cm (1 dm) on each side. A liter is thus equal to both 1000 cm3 (10 cm × 10 cm × 10 cm) and to 1 dm3.

Litre (l), also spelled liter, unit of volume in the metric system, equal to one cubic decimetre (0.001 cubic metre). From 1901 to 1964 the litre was defined as the volume of one kilogram of pure water at 4°C (39.2 °F) and standard atmospheric pressure; in 1964 the original, present value was reinstated. 

Britannica.com

Relative Density

As per the Wikipedia , Relative density of Specific gravity is the ratio of the density of a substance to the density of a given reference material. Specific gravity is nearly always measured with respect to water at 4 °C .

If a substance’s relative density is less than 1 then it is less dense than the given substance.

If greater than 1 then it is denser than the given substance.

If the relative density is exactly 1 then the densities are equal; that is, equal volumes of the two substances have the same mass.

Illustrations

Example-1 For Water, relative density is 1 . So its one Kilogram is just equal to one Litre at 4 °C.

i.e. In one litre bottle of Water contents 1 kg .

Example – 2 For Ghee, Relative density is 0.905 and density is 0.905 kg/ Litre. So its value in kg is less than litre.

Mass = Volume x Density

Mass = 1 Litre x 0.905 Kg/ Litre

Mass = 0.905 Kg = 905 gm.

Note Due to less density than water, ghee floats in water.

Similarly we may find the relation of other material if we know its relative density

i.e. In one litre bottle of ghee contents 0.905 kg .

Example – 3 For Mercury, Relative density is 13.5 and density is 13.6 kg/ Litre. So its Mass of Mercury in kg of one Litre Mercury

Mass= Volume x Density

Mass= 1 Litre x 13.6 Kg/ Lt.

Mass = 13.6 Kg

i.e. In one litre bottle of mercury contents 13.6 kg .

Relative Density Chart.

Conclusion:-

Therefore, we can now conclude that the mass of a liquid ( in kilogram) that floats in water is less than its volume ( in litre in litre. Similarly the mass of a liquid( in kilogram) which sinks in water is greater than its volume ( in litre). Thus the density of former is less than later one.

How much does 1 Litre of water weigh in KG?

Does 1 Litre of milk weigh 1 kg?

How many litres is 1 kg?

Is 1 liter the same as 1 kg?