# Yeast Calculator

![Calculate how many yeast packages to add or how big of a starter to make](https://559214094-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LEzhWP2LGeXaKgS2qr4%2F-LFRyl_P6JbL2o6antht%2F-LFRz7vV7GrzRxnwYWEd%2Fimage.png?alt=media\&token=3290722d-2721-4f7b-9213-16ae612c7601)

### PurePitch

Formula for calculating viability for White Labs PurePitch® yeast packets is based on official data found here: <https://www.whitelabs.com/news/purepitch-shelf-life>

Average viability of PurePitch® pure liquid yeast over a period of six months:

| Time     | Viability |
| -------- | --------- |
| 1 month  | 99.21%    |
| 2 month  | 98.05%    |
| 3 month  | 90.26%    |
| 4 months | 84.28%    |
| 5 months | 79.35%    |
| 6 months | 71.59%    |