How much should I spend on a wedding gift?

Im 20 and engaged to be married next year. Im living in ontario canada and i you give enough to pay for your meal and a gift on top of that. the meal is 100 dollars. and a gift of as much as you can afford. so if you are invited to a wedding and you have 2 kids and a partner its 400 plus a gift of 100 so a family of 4 would be 500 bucks...