Formula Calculation Problems and Solutions. Absorption costing is linking all production costs to the cost unit to calculate a full cost per unit of inventories. Overhead Ratio Double Entry Bookkeeping Definition Formula Calculation and. . It is sometimes called the full costing method because it includes all costs to get. This costing method treats all production costs as costs of the product regardless of fixed cost or variance cost. The formula used in computing the rate is. The machine hour rate is similar to the labour hour rate method and is used where the work is performed primarily on machines. Factory overheadMachine hours If factory overhead is Rs 3 00000 and.