Have you tried the Google calculator...It converts virtually everything to everything.
Go to the google home page and type in
250 grams in kilograms
or
1000 grams in kilograms...
(1000 grams equals 1 kilogram by the way)
You can convert Kilometres to miles and hectares to acres all sorts of stuff...It even does aritmetic for you as well just type a 25 x 4 for example and click search....