Count values of a column

I've got two database tables:

Persons
id   user   product
1     1       3
2     1       5
3     1       7

products
id   kilo
3     8
5     15
7     3

I'm wondering how to count values from a database, in this case I want to get the total kilo's of products for user 1. The result should be '26'. Is this possible?

SELECT kilo FROM `products` WHERE `id` IN (SELECT `product` FROM `person` WHERE `user` = '1')