Most non-refundable credits are calculated at 15% federally (the lowest tax rate). There are exceptions for donations and some provincial credits but generally the amount of the credit applied to your tax owing is 15% of the credit itself. This is because the credit is applied to your tax owing (which is calculated using the various tax brackets).

You can see the calculation for your federal tax owing, including the amount of all your non-refundable credits, on your PDF copy of your return - specifically Schedule 1.