Sourdough Starter Calculator
Work out feeding ratios and how much starter to build for a bake.
Please note: Cooking guides only. Times and temperatures vary with oven calibration, altitude, starting temperature and cut. For anything where safety matters — poultry, pork, sous vide, preserving — use a probe thermometer and follow your national food safety guidance rather than a calculated time.
What the Sourdough Starter Calculator does
A starter feed is described as a ratio of existing starter to fresh flour and water. Dividing the target weight by the total number of parts gives what each part weighs, and from there the three amounts follow directly.
Formula
Total parts = Starter + Flour + Water partsPer part = Target weight ÷ Total partsSeed = Per part × Starter partsFeed multiple = Total parts ÷ Starter parts
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Calculate | one of 2 options | Yes | — |
| Starter you want to end up with | g | Yes | Accepts more than 0. |
| Ratio — starter part | number | Yes | Accepts 0.1 or more. |
| Ratio — flour part | number | Yes | Accepts 0.1 or more. |
| Ratio — water part | number | Yes | Accepts 0.1 or more. |
| Starter you have | g | Optional | Optional — shows how much discard you will have. Accepts 0 or more. |
How to use it
- Choose Calculate.
- Enter Starter you want to end up with, Ratio — starter part, Ratio — flour part and Ratio — water part.
- Optionally add Starter you have.
- Select Calculate.
Worked example
Building 200 g of starter on a 1:4:4 feeding ratio.
- Target
- 200 g
- Ratio
- 1:4:4
Nine parts in total, so each part is 22.2 g. Use 22.2 g of starter with 88.9 g flour and 88.9 g water.
Frequently asked questions
What feeding ratio should I use?
1:1:1 for a quick refresh before baking, 1:4:4 or 1:5:5 for an overnight build. Larger ratios take longer but produce a milder, less sour loaf.
Do I have to discard?
Only what you cannot feed. Discard exists because feeding everything you have would need ever-growing amounts of flour — but the discard itself is perfectly good in pancakes or crackers.
Method and sources
Method. Seed, flour and water split from the target weight according to the feeding ratio entered, with the resulting hydration computed including what the seed itself contributes.
Assumptions
- The starter is at the hydration assumed when accounting for the flour and water it carries.
Limitations
- Timing is temperature-driven and not modelled. The same feed peaks in a few hours in a warm kitchen and overnight in a cold one.
- A starter's activity depends on its maturity and culture, neither of which arithmetic can see.
Sources
- None — ratio arithmetic on the reader's own feeding schedule — Not applicable. Recorded so the lack of a citation is legible as intentional.