Project Material Waste Calculator
Add a waste allowance for cuts, mistakes, and unusable offcuts to your project's required material amount, so you buy enough on the first trip.
How the overage is worked out
One multiplication, applied to whatever unit you pick:
total to buy = amount needed × (1 + waste % / 100)
extra = total to buy - amount neededThe defaults - 100 sq ft at 10% - come back as 110.00 sq ft, of which 10.00 is the allowance. The unit is a label only - sq ft, linear ft, board feet, sheets and gallons all run through the same arithmetic. A waste figure of 0 returns your input unchanged; a required amount of 0 or less is rejected.
Picking a percentage, and rounding after it
Waste is not one number. It is the sum of the material a blade destroys, the offcuts too short to use, and the pieces you cut twice:
| Situation | Usual allowance |
|---|---|
| Square cuts from dimensional stock | 10% |
| Sheet goods cut to a parts list | 15% |
| Grain or pattern to match, diagonal layouts | 20% |
| Rough hardwood you still have to joint and square | 30-40% |
Grain direction is the reason sheet-goods waste runs high: if every face has to read the same way, the parts can only nest one way round, and the leftover strip down one edge is scrap rather than stock. Then round up to what is actually sold. 110 sq ft of plywood is 3.44 sheets at 32 sq ft each, so you buy 4 - a real 28% overage, not 10%.
Frequently asked questions
How much extra plywood should I buy?
About 15% for a normal parts list, 20% if the grain has to run one way on every visible face. Then round up to whole sheets, which usually adds more than the percentage did.
Is 10% waste enough for hardwood?
Not for rough-sawn boards. Between crook, cupping, split ends and the edges you lose jointing, 30% is a fairer figure, and 40% if you are cutting around knots for clear stock.
Does the answer include saw kerf?
Only if you built it into the percentage yourself. The tool applies a flat multiplier and knows nothing about how many cuts you are making.