How much oil do i use in place of butter in a cake?
Butter is around 80% fat so for your 10tbsp, 8tbsp of oil and 2 of water (or milk) would be closest. The texture and flavour will never be exactly the same using oil as butter, so on the rare occasions I want to use oil in a cake, I look for a recipe for that type of cake that uses oil.

Measuring butter in tablespoons, unless it's already melted, isn't very accurate, so perfect substitution probably isn't required for the texture in this case.