Calculator
Yeast calculator for your fermentation time
One yeast dose for the hours and dough temperature you actually have. The result is a starting percentage of flour weight, not a promise that the dough has doubled.
Quick answer. For the default 12 hours at 21.1°C (70°F) and 1000 g of flour, this is 0.05% instant yeast, 0.5 g.
Yeast
0.05% instant yeast, of flour weight
| Yeast | % of flour | Weight |
|---|---|---|
| Instant yeast | 0.05% | 0.5 g |
| Active dry yeast | 0.061% | 0.61 g |
| Fresh yeast | 0.152% | 1.52 g |
The formula
instant % = 0.05 × 12 ÷ Σ (hours × 2^((°C − 21.1) / 10))
21.1°C is 70°F. At that temperature for 12 hours, the formula returns 0.05% instant yeast. For 1000 g of flour that is 0.5 g instant. The same 12 hours, 10°C colder, returns 0.1% — double the yeast, because the rate is assumed to halve.
The anchor is a published checkpoint from TXCraig, Baker’s yeast quantity prediction model, pizzamaking.com, topic 26831: about 0.05% instant yeast at 70°F takes 12 hours. Craig’s chart then uses a fitted growth curve. This page keeps the checkpoint and uses a plain Q10 rule everywhere else: fermentation rate doubles for each 10°C warmer. Two stages share one yeast dose. Add hours × rate for each stage, then divide.
Limits
- This is commercial yeast only. It is not a sourdough model.
- Below about 10°C the doubling rule is rough. A warm finish is a second stage. It is not hidden inside the fridge rate.
- Under about 2 hours, yeast is still waking up, so you may need more than the estimate.
- Past about 72 hours, cells have been multiplying and a straight inverse of time gets less reliable.
- Salt, sugar, oil, and the flour itself are not inputs. The anchor is a moderate pizza dough, not a sweet dough and not a very salty one.
- “Ready” means a moderate pizza ferment near that checkpoint. It is not a measured doubling, and it is not a loaf that has tripled.
Active dry and fresh weights use King Arthur’s professional factors: instant = fresh × 0.33, active dry = fresh × 0.40. On a long ferment the practical gap between active dry and instant is smaller than that. King Arthur’s home-baking guidance sometimes treats them as equal.
Questions
- How much instant yeast do I need for 12 hours at room temperature?
- At the anchor — 12 hours at 21.1°C (70°F) — the formula returns 0.05% instant yeast. For 1000 g of flour that is 0.50 g. The checkpoint is TXCraig’s published figure on pizzamaking.com, topic 26831: about 0.05% instant yeast at 70°F takes 12 hours. “Ready” here means a moderate pizza ferment near that checkpoint, not a measured doubling.
- Does colder dough need more yeast for the same time?
- Yes, in this model. The rate doubles for every 10°C warmer, so a colder stage needs more yeast to finish in the same number of hours. The same 12 hours, 10°C colder, returns twice the yeast. Below about 10°C that doubling rule is only a rough guide.
- How do I calculate yeast for the fridge and then the counter?
- Turn on the second stage. Enter the cold hours and the dough temperature in the fridge, then the room-temperature hours and temperature. The formula adds hours × rate for each stage and uses one yeast dose for both. A warm finish is not hidden inside the fridge rate.
- What does ready mean in this yeast calculator?
- The anchor is a moderate pizza dough: 0.05% instant yeast for 12 hours at 21.1°C (70°F), from TXCraig’s baker’s yeast chart on pizzamaking.com. It is not a measured doubling, and it is not tuned for a very sweet or very salty dough.
- Can I use this yeast calculator for sourdough?
- No. The model is for fresh, active dry, or instant yeast. A starter does not convert to a yeast weight in any reliable way. The conversion page splits a starter into flour and water. The baker’s percentage calculator keeps that water inside the hydration.
- Why is active dry a different weight from instant yeast?
- This page converts with King Arthur’s professional factors: instant = fresh × 0.33 and active dry = fresh × 0.40. King Arthur’s home-baking guidance sometimes treats active dry and instant as equal on a long rise. The practical gap is often smaller than the factor. The page still shows the professional weights.
Last reviewed 1 November 2026.
Sources
The 0.05% / 12 hour / 70°F checkpoint is TXCraig’s. Temperatures away from that point use this page’s Q10 rule, which is not his fitted curve. Active dry and fresh weights use King Arthur’s professional factors.