56.4 kg is equivalent to 8 stones and 12.3407lbs.
The stone is a unit of weight and mass. It is part of the Imperial system of weights and measures used in the British Isles formerly used in most Commonwealth countries.
It is equal to 14 pounds avoirdupois or 6.35029318 kilograms. Eight stone make a hundredweight in the Imperial system.
The plural form of stone is correctly 'stone,' though 'stones' is sometimes used, not usually by natives of the British Isles. The abbreviation is st.
Historically, the stone was used for weighing agricultural commodities. For example, potatoes were traditionally sold in stone and half-stone (14-pound and 7-pound quantities).
Although no longer an official unit of measure the stone remains universal within the British Isles as a means of expressing human body weight.