Three forms of one organism, and why the weights differ
Fresh, active dry and instant yeast are all Saccharomyces cerevisiae. What separates them is water and processing. Fresh compressed yeast is a moist cake at roughly 70% water, so most of what you weigh is not yeast at all. Active dry yeast is dried to around 6-8% moisture in a way that leaves an outer layer of dead cells, which is why it is traditionally rehydrated before use. Instant yeast is dried faster into finer particles with fewer dead cells and added emulsifier, and it can be mixed straight into the flour.
That is the whole basis of the conversion: you are compensating for water and for viable cell count. Take three times the weight of fresh yeast to match instant, and around one and a half times for active dry. Those factors are approximations of a biological quantity, not physical constants, which is why two conventions circulate. Bakery texts generally use 1 : 1.5 : 3 for instant : active dry : fresh; packet guidance from several manufacturers implies a milder 1 : 1.25 : 3, on the grounds that modern active dry has a higher live-cell count than the product those older rules were written for. The gap between them is about 17% on the active dry figure — enough to notice on a long ferment, not enough to ruin a loaf.
The one figure that travels across all recipes is baker's percentage: yeast weight divided by total flour weight. Quote a dose that way and it survives conversion between yeast forms, batch sizes and unit systems, which is why every professional formula uses it.
The formula, and how to use packets and teaspoons safely
Assign each form a factor relative to instant yeast, then the conversion is one multiplication and one division: target weight = your weight × factor(target) ÷ factor(what you have). Going from fresh to instant divides by 3; going from instant to fresh multiplies by 3; going between the two dry forms uses the ratio of their factors.
Volume is the awkward part. Dry yeast is sold in 7 g (¼ oz) packets that are labelled as 2¼ teaspoons, which implies about 3.1 g per level teaspoon. That figure is close enough for both instant and active dry, since manufacturers package both to the same net weight and the same nominal spoon measure. It is still a volume measure of a granular solid, so it varies with how you fill the spoon — scooping compacts the granules and can add a fifth to the dose.
Fresh yeast cannot be spooned meaningfully. It is a moist solid that compresses, and any teaspoon figure for it would be fiction. Buy it by the cake instead: the small retail cake is 0.6 oz (about 17 g) and the larger one is 2 oz (about 56.7 g); bakery blocks are usually 500 g or 1 lb. The calculator reports fresh in cakes rather than teaspoons for that reason.
A note on what the conversion does not preserve: it matches leavening power at the moment of mixing, not fermentation behaviour end to end. Fresh yeast starts faster and fades sooner; instant is slower off the mark and more even across a long bulk. On a two-hour straight dough the difference is small. On a twelve-hour retard it is visible, and bakers often trim the converted dose rather than match it exactly.
Worked example: a formula written for fresh yeast
You have a bakery formula calling for 30 g of fresh yeast on 1,000 g of flour, and you keep instant yeast at home. Using the bakery convention:
- Read the factors. Fresh is 3; instant is 1.
- Convert. 30 × 1 ÷ 3 = 10 g of instant yeast.
- In teaspoons. 10 ÷ 3.1 = 3.23 level teaspoons, so a shade over three.
- In packets. 10 ÷ 7 = 1.43 packets — one full packet plus a bit under half of a second.
- In ounces. 10 ÷ 28.35 = 0.353 oz.
- Baker's percentage. 10 ÷ 1,000 × 100 = 1.00%, a normal same-day dose.
Check the third form while you are here: active dry at the bakery convention is 10 × 1.5 = 15 g, or 4.84 teaspoons, which is 1.50% of flour. The original fresh figure, 30 g, is 3.00% of flour — and that is why comparing raw yeast percentages between recipes is meaningless unless you know which form the author meant.
Now suppose you switch to the packet convention because your active dry is a modern product. Converting the same 10 g of instant gives 10 × 1.25 = 12.5 g of active dry rather than 15 g. Working backwards, 10 g of active dry converts to 8 g of instant on the packet convention but 6.67 g on the bakery one. If your dough is consistently rising faster or slower than the formula predicts after a conversion, the convention is the first thing to check.
What dose is normal, and how to read the percentage
Read the baker's percentage, not the gram figure, because the gram figure is meaningless without the batch size. On instant yeast, ordinary same-day white bread sits around 0.6-1.2% of flour; enriched doughs such as brioche and sweet buns run higher, often 1.5-2.5%, because sugar and fat slow the yeast; and long or cold-retarded ferments run much lower, sometimes 0.1-0.3%, because the yeast has all night to work. Multiply those by 1.5 for active dry and by 3 for fresh to get the equivalent bands in those forms.
A dose above about 3% of flour on instant is worth a second look. It is not impossible — some very sweet, very heavily enriched doughs go there — but far more often it means the flour weight was entered wrong or a fresh-yeast figure has been used without converting.
Going the other way, a dose under about 0.1% instant is a preferment-style dose. At that level the dough behaves like one built on a poolish and the timing depends heavily on temperature, which is exactly when the desired dough temperature calculator earns its keep — a couple of degrees of mixing temperature will move a twelve-hour bulk by more than a small change in yeast will.
If you are converting between commercial yeast and a sourdough levain, there is no weight conversion at all: the organisms and the acidity are different, and a levain leavens on a different clock. The workable approach is to design the sourdough on prefermented flour rather than on yeast equivalence, which the sourdough levain build calculator sizes for you. Bakers who spike a sourdough with a little commercial yeast typically use 0.1-0.2% instant on top of the levain, which shortens the bulk without flattening the flavour.
Equivalent yeast doses by form and package
| Instant | Active dry | Fresh | Instant in tsp | Instant in packets | Baker's % on 1,000 g flour |
|---|---|---|---|---|---|
| 1 g | 1.5 g | 3 g | 0.32 | 0.14 | 0.10% |
| 2 g | 3 g | 6 g | 0.65 | 0.29 | 0.20% |
| 3.1 g | 4.65 g | 9.3 g | 1.00 | 0.44 | 0.31% |
| 5 g | 7.5 g | 15 g | 1.61 | 0.71 | 0.50% |
| 7 g (1 packet) | 10.5 g | 21 g | 2.26 | 1.00 | 0.70% |
| 10 g | 15 g | 30 g | 3.23 | 1.43 | 1.00% |
| 17 g | 25.5 g | 51 g (3 cakes) | 5.48 | 2.43 | 1.70% |
| 20 g | 30 g | 60 g | 6.45 | 2.86 | 2.00% |
On the packet convention every active dry figure falls to 1.25 times the instant column instead of 1.5 — for example 10 g instant becomes 12.5 g rather than 15 g.
Mistakes that cost you a rise
- Substituting one for one. Using 30 g of instant where a formula wanted 30 g of fresh triples the dose. The dough will race, then collapse, and taste yeasty.
- Comparing yeast percentages between recipes without checking the form. A 3% yeast recipe and a 1% yeast recipe can be identical if one is written for fresh and the other for instant.
- Dissolving instant yeast in hot water. Instant is designed to go into the flour dry. If you do rehydrate it, keep the water below about 110 °F (43 °C) — the temperatures recommended for active dry will damage instant, which prefers cooler water.
- Scooping teaspoons instead of levelling them. A scooped, compacted teaspoon can hold a fifth more granules than a levelled one. Weigh when the dose is under about 5 g.
- Using fresh yeast past its window. Fresh yeast loses activity quickly in the fridge and is generally good for two to three weeks. If it has darkened, dried at the edges or smells sour, the conversion factor no longer applies.
- Salting yeast directly. Salt dehydrates yeast cells on contact. Keep the two apart in the bowl until the flour and water go in, regardless of which form you are using.
- Forgetting that the water balance changes. Fresh yeast is roughly 70% water, so swapping 30 g of fresh for 10 g of instant takes about 20 g of water out of the dough — two points of hydration on a 1,000 g flour batch.
Baker's percentage is the only portable form
Whenever you record a formula, write the yeast as a percentage of total flour and name the form: "0.8% instant", not "8 g yeast". That single habit removes almost every problem this calculator exists to solve, because it survives batch scaling, unit changes and yeast substitution. It also lets you compare your dough directly against a published formula in a book, which is otherwise impossible when one is written in packets and the other in grams of fresh.
Key terms
- Compressed (fresh) yeast
- Yeast cream pressed into a moist cake at roughly 70% water. Sold refrigerated in 0.6 oz and 2 oz retail cakes and in 500 g or 1 lb bakery blocks; short shelf life.
- Active dry yeast
- Yeast dried to a coarse granule with a layer of dead cells on the outside. Traditionally rehydrated in warm water before mixing, which dissolves that layer away.
- Instant yeast
- Finer, faster-dried yeast with fewer dead cells and an added emulsifier. Mixed straight into the flour. Sold as SAF Instant, rapid-rise, bread-machine and similar names.
- Osmotolerant yeast
- An instant yeast strain selected for sweet doughs, sold as SAF Gold and similar. Use it where sugar exceeds about 10% of flour; the weight conversions here still apply.
- Baker's percentage
- Any ingredient expressed as a percentage of total flour weight. The only form in which a yeast dose can be compared across recipes.
Where yeast dose sits among your other controls
Yeast quantity is the fastest lever on fermentation speed, but it is not the only one and rarely the best one. Dough temperature moves fermentation rate roughly as much per 8-10 °F as a doubling of yeast does, and it costs nothing; the desired dough temperature calculator gives you the water temperature to hit a target. Salt is a brake — the difference between 1.8% and 2.2% is visible on a long bulk. And hydration changes how fast gas moves through the dough as much as it changes how the dough feels.
If your goal is flavour rather than speed, cutting the yeast and lengthening the ferment does more than any substitution between forms. A dough at 0.2% instant fermented overnight tastes markedly different from the same formula at 1% in two hours, because the slower ferment produces more of the organic acids and alcohols that make bread taste of something. That path leads naturally to preferments, and from there to sourdough, where the sourdough levain build calculator and the sourdough starter hydration calculator take over the arithmetic.
Pizza is the case where yeast doses look strangest to bread bakers, because most pizza dough is cold-fermented for one to three days and the doses fall accordingly — often 0.1-0.4% instant. There the harder question is portioning, which follows pan area rather than any fermentation logic; the pizza dough thickness factor calculator handles that side.
Two limits on this calculator. The factors are industry conventions rather than measured cell counts, and a specific brand may sit either side of them. And the conversion says nothing about shelf life or storage: instant yeast keeps for years frozen in a sealed jar, active dry for a year or two, and fresh for two or three weeks refrigerated. A conversion applied to yeast that has lost half its activity will still under-leaven, no matter how careful the arithmetic.