# Production Material Requirement Calculator

> Work out how many units to start and how much material to order to finish a target number of good units after an expected scrap rate.

Category: Manufacturing & packaging · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/production-material-requirement-calculator

If a share of what you start is scrapped, you must start more than you need. Divide the good units required by (1 − scrap rate), then multiply by material per unit.

Also called: Scrap allowance calculator, Raw material requirement calculator.

## Inputs
- Good units required (default 10000)
- Expected scrap (share of units started) (unit %; default 4)
- Material per unit (default 0.25)
- Material already in stock (default 500; optional)

## Results
- Units to start
- Gross material required
- Material to order (after stock)
- Expected scrapped units

## Formula

```
Starts = ⌈Good ÷ (1 − Scrap%)⌉;  Gross material = Starts × Material per unit;  Net = Gross − Stock
```

Where:
- Scrap%: share of units started that end up scrapped

## Worked example
1. Starts = 10,000 ÷ 0.96 = 10,416.7, rounded up to 10,417.
2. Material = 10,417 × 0.25 = 2604.25.
3. To order = 2604.25 − 500 = 2104.25.

**Result:** To finish 10,000 good units at 4% scrap, start 10,417 and order 2104.25 units of material.

## What the result means

Dividing by (1 − scrap) is not the same as adding the scrap percentage: adding 4% would give 10,400 starts and leave you short.

## Assumptions and limits
- Scrap is a share of units started, not of good units.
- Every unit uses the same material, whether it ends up good or scrap.
- For multi-step processes, apply each step’s scrap rate in turn, starting from the last step.

## Questions

### Why not just add 4%?

Because the 4% is lost from the larger starting quantity. 10,400 × 0.96 = 9984, short of 10,000.

### What if my scrap rate is quoted on good output?

Then multiply good units by (1 + rate) instead.

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Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/production-material-requirement-calculator