# How the cost is worked out

## The formula

**Cost per part** = spool price ÷ (spool weight in kg × 1000) × part weight in g × (1 + waste ÷ 100)

The total multiplies that by the quantity. **Spools needed** is the total filament, waste included, divided by the spool weight, rounded up.

## Example

A 1 kg spool at $25 CAD costs 2.5 cents a gram. A 50 g part is $1.25 of filament, or about **$1.31** with 5% waste. Ten of them use 525 g: $13.13 and one spool.

## Choosing the waste allowance

| Print | Allowance |
| --- | --- |
| One colour, no supports | 3 to 5% |
| One colour with supports | 5 to 10% (or use the slicer's weight, which includes supports) |
| Multi-colour with purging | Use the purge weight your slicer reports, often 20% or more |

## What it doesn't include

Filament only. Electricity, machine time, wear, packaging and your time aren't in this number; add them separately when you price a job.