What this calculation means
Portion-size impact compares a current and proposed portion using one fixed cost per purchase or usable unit. It isolates the quantity change.
The cost basis is held fixed. If a changed portion also changes yield, preparation, or unit price, that effect is outside this comparison.
How to use this calculator
Enter the unit cost, current and new portion quantities, and the number of portion units in one cost unit. Keep both portions in the same unit.
Formula and variables
Portion cost = Cost per unit × Portion quantity ÷ Units per cost unit; Change = New portion cost − Current portion cost
- Cost per unitUSD / unit
- Cost per weight or volume unit.
- Current portionunit
- Current portion size.
- New portionunit
- Proposed portion size.
- Units per cost unitunit
- For example, 16 ounces per pound. Use 1 when units already match.
Dollar amounts display to cents, with exact half-cent values rounded away from zero; intermediate calculations keep full precision.
Understand your result
The primary result is the new portion cost. The detail also gives current cost and the dollar change per portion.
Worked example
Unit cost is $2/lb; portion changes from 4 oz to 6 oz.
Cost per unit: 2 USD / unit
Current portion: 4 unit
New portion: 6 unit
Units per cost unit: 16 unit
- The cost per ounce is $2 per lb ÷ 16 = $0.125.
- Current portion: 4 × $0.125 = $0.50. New portion: 6 × $0.125 = $0.75.
- The new portion costs $0.25 more.
Example result: $0.75 / new portion
Frequently asked questions
When should Units per cost unit be 1?
Use 1 when the cost unit and portion unit already match. Use 16 for a cost per pound and portions measured in ounces.
Is the large displayed amount the cost change?
No. The primary amount is the new portion cost. The current portion and the difference are separately labelled in the result details.