Contribution margin ratio is overall total contribution margin while contribution margin ration per unit is the allocation of total production contribution margin to per unit basis.

Formula for calculating average Contribution margin

Average contribution margin = total contribution margin / total number of units

Contribution margin for per machine hour is as follows:

total contribution margin / number of machine hours = contribution margin per hour

Contribution margin per unit = Contribution margin / number of units of products

Contribution margin ratio = Contribution margin / Net sales

The formula is different for both situations because contribution margin per unit calculates the contribution margin for one unit of product while contribution margin ratio calculates the contribution margin for total overall sales as overall sales may be included different mix of products with diff rent fixed and variable costs that's why both of these are calculated separately

Formula for Breakeven point:

Breakeven point = Fixed Cost / Contribution margin ratio

Contribution margin ratio = Sales / contribution margin

Contribution margin = sales - variable cost