Use cases
This calculator is designed for bakers who:
- Want to fit baking into a busy schedule by calculating how much yeast or starter fits a chosen timeframe.
- Need to adapt a recipe for a different kitchen temperature.
- Want to combine warm bulk fermentation with cooler stages in separate schedule steps.
- Need ripe starter/levain as baker's % of total formula flour (not seed starter in a levain build).
Already have a commercial yeast amount and need Instant ↔ Active Dry ↔ Fresh (or grams ↔ teaspoons)? Use the Yeast Conversion Calculator. That tool is a separate commercial-yeast substitution calculator — it does not size leavening from time and temperature.
Commercial yeast mode
Yeast activity roughly doubles every 10–14°F rise in temperature. Commercial mode uses a TXCraig1 Instant Dry percentage table with a 14°F doubling rate to accumulate effective fermentation time across stages, then scales to Active Dry or Fresh with TXCraig1 type multipliers.
When you add multiple stages (e.g. 4 hours at 72°F followed by 24 hours at 39°F), the calculator accumulates progress toward full proof and returns baker's-% yeast. Optionally enter total flour to see grams.
Yeast type factors (commercial mode)
After looking up Instant Dry baker's %, commercial mode scales to other yeast forms with TXCraig1 multipliers:
| Yeast type | vs Instant |
|---|---|
| Instant Dry (IDY) | 1.00× |
| Active Dry (ADY) | 1.3125× |
| Fresh / Cake Yeast | 3.125× |
Sourdough starter mode
Sourdough mode uses a separate TXCraig1 model built on microbial growth equations from Gänzle et al., fitted by Craig Lindberg (TXCraig1) for baker's schedules. The runtime math matches TXCraig1's exported multi-stage spreadsheet: temperature enters a polynomial for doubling time; stage doublings sum; starter fraction is 0.894 / 2^totalDoublings.
The result is whole ripe starter/levain as baker's % of total formula flour. It is not PizzaBlab's separate "% Starter in Levain" seed/feed setting used when building a preferment.
Confidence is highest near 65–75°F. Cold or hot stages, very high (>40%) or very low (<1%) starter, and dough that has not yet reached ambient temperature all deserve empirical adjustment for starter strength, flour, hydration, salt, and dough mass.
Model equations
TXCraig1's 75°F regression uses H₇₅(p) = −5.368 × ln(p) − 0.6014, where p is a fraction (0.20 means 20%). Its inverse is p = exp(−(H₇₅ + 0.6014) / 5.368).
Y(T) = 0.0124 × (36 − T)^2.981 × exp(−0.3355 × (36 − T))
L(T) = 0.1267 × (41 − T)^1.5404 × exp(−0.1931 × (41 − T))
G(T) = Y(T) + 0.5 × L(T)
r(T) = G(T) / G(23.9)
Here T is °C. LAB activity is weighted at 50% as Y + 0.5L, not averaged equally. These continuous equations document the source model; the calculator uses the exported spreadsheet's polynomial doubling-time fit at runtime so its results match published spreadsheet cases.
Sources & attribution
Commercial yeast sizing and the sourdough starter model are based on work by Craig Lindberg (TXCraig1) on the Pizza Making Forum starter-model thread, including its multi-stage spreadsheet. Production starter math follows that exported spreadsheet polynomial for parity with published cases.
The continuous microbial form references Gänzle, Ehmann, and Hammes' 1998 paper, Modeling of Growth of Lactobacillus sanfranciscensis and Candida milleri.
PizzaBlab's public sourdough calculator is a helpful implementation reference for bakers exploring these ideas. Baking Maths implements spreadsheet-parity TXCraig1 math directly and keeps commercial yeast and sourdough as separate modes because they are separate models.