what is 5 liters in kilograms?

The mass of 5 L of a substance depends on the density of the substance.

For example, the density of water is 1 kg/L, then
Mass of 5 L of water = (5 L) × (1 kg/L) = 5 kg

One more example, the density of mercury is 13.6 kg/L, then
Mass of 5 L of mercury = (5 L) × (13.6 kg/L) = 68 kg

Depends on the density of the material.
For example, 5 litres of mercury weigh 13.7 times 5 litres of water.

5 liters of lead has a mass of about 56.7 kilograms.
5 liters of air has a mass of about 0.0064 kilograms.
Most things are somewhere between those two values.

of what substance? water is 1 kg per liter, so five liters of water is 5 kg of water, although water purity, temperature, and pressure will affect that value slightly. You need to know the substance, its physical state, and the conditions of the system, in order to know the density. Once you have density, then mass is just density times volume.

liters is a measure of volume.
kg is a measure of weight

5 liters
Conversion is dependent on the density of the liquid.

'litres' is a measure of (liquid) volume
'kilograms' is a measure of ' weight/mass'.

You need to know the density of the substance in order to change litres to kilograms.

It does not convert directly, you need to know what liquid you are measuring