Recipes are written for whatever yeast the author had on hand: fresh yeast in many European books, active dry in older American ones, instant in most modern recipes and a sourdough starter in countless others. Converting between them is simple arithmetic once you know the ratios. This guide gives the ratios LoafCalc uses, explains why other charts sometimes disagree and shows how to switch a whole recipe between commercial yeast and sourdough.
The three kinds of commercial yeast
- Fresh yeast, also called compressed or cake yeast, is a moist block of live yeast that is about 70% water. It is perishable, lasting a couple of weeks in the refrigerator, and is crumbled into the dough or dissolved in some of the recipe's water.
- Active dry yeast is dried into larger granules. It is traditionally dissolved in lukewarm water before use, though modern active dry can usually be mixed in dry when the dough has a reasonably long rise.
- Instant yeast, sold as instant, rapid-rise or bread machine yeast, has finer granules and goes straight into the flour. It is the most concentrated of the three by weight.
Conversion ratios by weight
LoafCalc converts commercial yeast using this ratio by weight:
fresh : active dry : instant = 3 : 1.25 : 1
Put another way:
- Active dry = instant × 1.25
- Fresh = instant × 3
- Instant = active dry × 0.8, or fresh ÷ 3
- Active dry = fresh × 0.417 (that is, 1.25 ÷ 3)
- Fresh = active dry × 2.4
| Instant | Active dry | Fresh | Instant, approx. teaspoons |
|---|---|---|---|
| 1 g | 1.25 g | 3 g | 1/3 tsp |
| 2 g | 2.5 g | 6 g | 2/3 tsp |
| 3 g | 3.75 g | 9 g | 1 tsp |
| 5 g | 6.25 g | 15 g | 1 2/3 tsp |
| 7 g (one 1/4 oz packet) | 8.75 g | 21 g | 2 1/4 tsp |
| 10 g | 12.5 g | 30 g | 3 1/4 tsp |
| 14 g | 17.5 g | 42 g (one European cube) | 4 1/2 tsp |
A standard US packet is 1/4 oz, which is 7.09 g; everyone rounds it to 7 g. The conversion works the same way in baker's percentages: a formula with 0.5% instant yeast needs 0.625% active dry or 1.5% fresh.
Why conversion charts disagree
You will find charts that put fresh to active dry at 2:1 rather than the 2.4:1 used here, and others that put fresh to instant at 2.5:1. There are a few reasons. Older active dry yeast was dried more harshly and carried a larger share of dead cells, so recipes compensated with more of it; modern active dry is much closer to instant. Fresh yeast's moisture varies by brand, and its strength fades the longer it sits in the refrigerator. Manufacturers also publish their own rounded figures for their own products.
The practical difference is smaller than it looks. With the 2:1 rule, 21 g of fresh yeast becomes 10.5 g of active dry instead of 8.75 g. That is 20% more yeast, which shortens fermentation somewhat rather than changing the bread, and a few degrees of dough temperature can easily matter as much. The desired dough temperature guide is worth reading alongside this one. Whichever ratio you use, judge proofing by the dough rather than the clock.
Measuring yeast by the teaspoon
Instant and active dry yeast both weigh about 3 g per teaspoon; a 7 g packet is 2 1/4 tsp, a little over 3.1 g per teaspoon. One-eighth of a teaspoon is about 0.4 g, which is handy for long, cold fermentations that call for tiny amounts. Fresh yeast does not measure well by volume, so weigh it. For quantities under a gram, a scale that reads to 0.01 g is the most accurate option.
Swapping commercial yeast for sourdough starter
There is no exact equivalence between commercial yeast and a sourdough culture. A starter's strength depends on its flour, feeding schedule and temperature and on how ripe it is when you use it. A rule of thumb still gives you a sensible starting point. A familiar one says that about 227 g (roughly 1 cup) of ripe starter replaces one 7 g packet of yeast. LoafCalc rounds that to:
1 g instant yeast ≈ 32 g ripe starter at 100% hydration
and, in baker's percentages:
levain % ≈ 32 × instant yeast %
| Instant yeast | Instant yeast per 500 g flour | Equivalent levain | Levain per 500 g flour |
|---|---|---|---|
| 0.25% | 1.25 g | 8% | 40 g |
| 0.5% | 2.5 g | 16% | 80 g |
| 0.6% | 3 g | 19.2% | 96 g |
| 0.75% | 3.75 g | 24% | 120 g |
| 1% | 5 g | 32% | 160 g |
Beyond about 30% levain the dough becomes noticeably acidic and can turn slack, so for fast same-day recipes with 1–2% instant yeast, don't follow the rule all the way up. Cap the levain at 20–30% and allow more time instead.
Converting a yeasted recipe to sourdough
Keep the total flour and total water the same, and take the starter's flour and water out of the final dough. Example: 500 g flour, 350 g water (70%), 10 g salt and 3 g instant yeast (0.6%).
- Levain: 0.6% × 32 = 19.2% of 500 g = 96 g of ripe 100% starter (the same as 3 g × 32).
- Split it: 96 g at 100% hydration = 48 g flour + 48 g water.
- Final-dough flour: 500 − 48 = 452 g. Final-dough water: 350 − 48 = 302 g.
- Leave out the yeast and keep the salt at 10 g.
| Ingredient | Yeasted | Sourdough version |
|---|---|---|
| Flour | 500 g | 452 g |
| Water | 350 g | 302 g |
| Ripe starter (100% hydration) | — | 96 g |
| Instant yeast | 3 g | — |
| Salt | 10 g | 10 g |
| Total flour / hydration | 500 g / 70% | 500 g / 70% |
The formula barely changes; the schedule changes a lot. Wild yeast is slower and less predictable than a packet, so expect bulk fermentation to take considerably longer than the yeasted recipe's first rise. Watch for the signs, such as a clear increase in volume, a domed and slightly jiggly surface and bubbles at the sides, instead of watching the clock. At a modest levain percentage the flavor shifts from plainly wheaty to gently tangy rather than sour. Our sourdough hydration guide shows how to do the split for a stiff starter.
When to keep a pinch of yeast
Some doughs benefit from both. Rich doughs with a lot of sugar and butter, such as brioche, can slow wild yeast to a crawl. A young or sluggish starter may not raise a loaf on its own, and sometimes you simply need a predictable timeline. In those cases add about 0.1–0.2% instant yeast (0.5–1 g per 500 g flour) alongside the levain. You keep most of the sourdough character and gain a more reliable rise.
Converting sourdough to commercial yeast
Run the rule backwards, instant yeast % ≈ levain % ÷ 32, and put the starter's flour and water back into the final dough. Example: 450 g flour, 325 g water, 100 g ripe starter at 100% hydration and 10 g salt.
- Total flour is 450 + 50 = 500 g and total water is 325 + 50 = 375 g, so the levain is 100 ÷ 500 = 20%.
- Instant yeast: 20 ÷ 32 = 0.625% of 500 g = 3.1 g, or 3.9 g active dry, or 9.4 g fresh.
- Yeasted version: 500 g flour, 375 g water, 10 g salt and 3.1 g instant yeast, still 75% hydration.
You will lose the sourdough tang and some keeping quality. To win back flavor, ferment part of the flour as a poolish overnight, or halve the yeast and give the shaped dough a long, cold rest in the refrigerator. If you're working in percentages, baker's percentage explained covers how preferments are counted.
The yeast converter does all of these conversions, including the sourdough equivalents, in grams or baker's percentages.