Mixing breast milk & powdered formula

[Bunnychan]

Does any mix bm & powdered formula in a feed, if so how do you do it? I've been mixing half carton & half BM by storing EBM in the bottle then topping up with a carton when needed but I'm wasting a lot of the carton. How would you go about using powdered instead?
I haven't got a clue about formula

Work out how much formula via the chart on the tin, deduct the volume of breast milk. Work out from the tin what proportion of water to powder. Mix the formula, add the booby milk. It's generally about 20-30 ml per scoop of powder, depending on brand.