Effect size for multiple regression?

Hi would anyone be able to explain to me what measure should be used to estimate an effect size in multiple regression? I want to do a power calculation based on effect sizes from my pilot (multiple regression), but not sure what statistic to use? Thanks
You should not use pilot data for determining effect size. These are almost certainly misleading.

The effect size in linear regression is usually Cohen's ƒ2, i.e. R²/(1-R²) .

With kind regards

Can I ask you also if you know what kind of statistic I should be looking at to see the effect sizes of individual predictors in a multiple regression?Thanks for your help.