USA/Canada flights operate on the piece concept, i.e. you can check two bags.
On all other flights the allowance is determined by weight alone.
You will be allowed two bags. If flying business these can each weigh up to 70 lbs, in economy they can weigh 50 lbs each. If you are in economy and have one bag of 70 lbs they might charge you for the 20 lbs overweight.
Actually, KL changed this recently to just one piece standard, with some factors allowing more. I saw my friend off to BOS from AMS last Sunday and sure enough, she was only allowed one piece of luggage. She had to pay €55 extra for the second. Both were about 23kg, btw. On the way over here, she was going to DEL so then she
was allowed an extra piece.
All can be found here:
http://www.klm.com/travel/nl_nl/prep...ance/index.htm (dutch).