How much sourdough starter do I need for one loaf?

For a standard loaf using about 500 g of flour, most recipes use roughly 100 g of ripe starter — that is about 20% of the flour weight. The amount is a percentage of your flour, not a fixed number, so it scales with the recipe. You can use anywhere from about 10% (50 g) for a slow, warm-kitchen rise up to 40–50% for faster, same-day bread.

Is more sourdough starter better?

No. More starter mainly makes the dough ferment faster, not better. A typical 20% gives a balanced timeline and flavour. Use more (25–50%) when your kitchen is cold or you want bread the same day; use less (10–15%) for a slower, more sour overnight rise in a warm kitchen.

What is the difference between starter and levain?

The starter (or mother) is the jar you keep alive and feed indefinitely. A levain is a small off-shoot you build from a spoonful of that starter and ripen for a few hours; the whole levain goes into the dough. When a recipe says "100 g starter", it almost always means the levain — the mother stays in the jar.

Does the starter change my dough hydration?

Yes. A standard 100% hydration starter is equal parts flour and water, so 100 g of starter adds 50 g of flour and 50 g of water to your dough. Your true hydration includes that water. A 70% added-water loaf with 20% starter lands around 73% total hydration.

How much sourdough starter do I need?

There isn't a single gram figure — the honest answer is a percentage of your flour, usually about 20%. For a normal loaf (around 500 g of flour) that's roughly 100 g of ripe starter — but anywhere from 10% to 50% works, depending on how fast you want it to rise and how warm your kitchen is.

~20%

of flour, typical

10–50%

workable range

~100 g

per 500 g loaf

Starter calculator

Enter your recipe's flour weight, then dial the starter amount. Everything below is a percentage of the flour — the way bakers actually scale.

Flour in your recipe (grams)

Starter 20% of flour

Standard — the classic ~20% almost every recipe starts from.

Water (hydration) 70%

Beginner-friendly and balanced — a forgiving place to start.

Salt 2%

Ripe starter (levain)100 g

Flour500 g

Water350 g

Salt10 g

Total dough960 g

Total hydration

72.7%

Includes the water already inside your starter.

Build it tonight

10 g ripe starter + 50 g flour + 50 g water → ~110 g levain (a 1:5:5 feed), ripe in 5–10 h at room temperature.

The calculator above is the quick answer. Below is the reasoning — what the percentage means, why it moves, and how to build the amount you need.

The trap in the question: starter vs levain

When a recipe says "add 100 g of starter," it almost never means tipping in your jar. It means a levain — a small off-shoot you build from a spoonful of your mother starter, feed once, and let ripen for a few hours. The whole levain goes into the dough; the jar you keep on the counter lives on.

How small is the spoonful? In Maurizio Leo's widely used Beginner's Sourdough at The Perfect Loaf (the independent site he launched in 2013; his 2022 cookbook is a James Beard winner), the 190 g levain is built from just 38 g of ripe starter plus fresh flour and water. Leo points out that the seed of mother starter is only about 0.8% of the recipe's flour — yet the levain it grows into is close to 20%. So "how much starter" really asks two different things, and the 20% answer is about the levain.

Why 20% is a starting point, not a rule

The starter is your engine. More of it ferments the dough faster; less ferments it slower. It barely changes how good the bread is — it changes the clock. That's why the same baker uses different amounts in summer and winter.

10–15% — slow, deep flavour. A warm kitchen, or a long overnight bulk.

~20% — the standard balance most recipes start from.

25–50% — faster. A cool kitchen, or bread you want the same day.

Temperature is the other half of the dial. The Perfect Loaf ripens its levain at 74–76°F (23–24°C) and aims for a final dough temperature near 78°F (25°C). Drop the room 5–6 degrees and the same 20% behaves like much less — which is exactly when you'd nudge it up. The classic home formula everyone converges on — used as the backbone by King Arthur Baking, Omni Calculator and The Perfect Loaf alike — is roughly 100% flour, 67% water, 20% starter, 2% salt.

The hidden water your starter smuggles in

A standard starter is 100% hydration — equal weights of flour and water. So 100 g of starter isn't 100 g of "flavour": it's 50 g of flour and 50 g of water hitching a ride into your dough. Your true hydration has to count that water.

Worked through: 500 g flour, 350 g added water (70%), 100 g starter and 10 g salt. Add the starter's 50 g of flour and 50 g of water to the totals and you get 550 g flour against 400 g water — a total hydration of about 72.7%, not 70%. The calculator above shows this line for whatever numbers you enter, so the dough you actually mix matches the dough you planned.

How to build the amount you need (without a giant jar)

You don't keep 100 g of starter sitting around — you build it the night before from a small seed. Bakers describe a feed as a ratio: 1:5:5 means 1 part old starter, 5 parts flour, 5 parts water. So 20 g of starter + 100 g flour + 100 g water makes about 220 g of fresh levain by morning — plenty for a loaf, with a little left to keep the jar going.

Bigger ratios (1:5:5, 1:10:10) use less of yesterday's starter and take longer to ripen, which is handy for an overnight build. The float test — a spoonful that floats in water — is the popular ripeness check, though it's imperfect; a starter that has roughly doubled, domed and smells tangy is the more reliable signal.

One reason this calculator is in grams

Sourdough is the one bake where cups quietly sabotage you. A cup of flour is 120 g by King Arthur's standard, but scoop straight from the bag and pack it down and the same cup can hit 140–150 g. That's a 20–25% swing in the single ingredient everything else is a percentage of — enough to turn a 70% dough into a stiff 60% one. A €15 kitchen scale removes the guesswork, which is why every figure here is a weight, not a volume.

Starter myth-buster

Three quick ones. Tap an answer to see why.

1. A recipe says "100 g starter". Roughly how much of your jar does that use up?

2. Your kitchen is cold (about 18°C). To keep the dough on schedule you should generally use…

3. A "100% hydration" starter means…

Sources & notes

Maurizio Leo, The Perfect Loaf — Beginner's Sourdough Bread (190 g levain from a 38 g ripe-starter seed; levain ripened at 74–76°F / 23–24°C; final dough temp ~78°F / 25°C). Site launched 2013; cookbook a 2022 NYT bestseller and 2023 James Beard winner.
The standard home baker's formula (~100% flour, 67% water, 20% starter, 2% salt) is the shared backbone of King Arthur Baking, Omni Calculator and The Perfect Loaf.
A 100% hydration starter is equal weights flour and water; total-hydration maths follows from including that flour and water in the totals.
King Arthur Baking — 1 cup of all-purpose flour weighs 120 g; scooping can push it 15–25% higher, the case for baking by weight.
Figures are starting points for a home kitchen; fermentation speed varies with temperature, flour and starter health.

Keep baking by the numbers

The question hides a better one. "How much starter?" really means "how fast do I want this to go" — and once you read 20% as a dial rather than a number, you stop following recipes and start steering them.