order unit in material master

heloo gurus

i created a material master in which i have taken material oil and base unit of measurement in litre. but in purchase order we have to taken units in kg. when i maintained order unit in material master in kg, it asks for thr the conversion fector . now i entered .910 kg= 1 litre but when i saved it .system gives massage that quanity cannot be taken in decimal it should be rounded up.

but our requirement is .910 kg= 1 liter. please help me out from this problem.

thanks