This free sourdough calculator handles the two bits of maths every baker gets stuck on: how much flour and water to feed your starter, and how much water, salt and starter to weigh out for a loaf. Pick a mode above, type your numbers in grams, and the amounts update as you go. New to sourdough? Start with my simple sourdough starter recipe, then come back here when it is time to bake.

Show every step at once

How much fed starter do you need?

Fed starter you want

When do you want it ripe?

Kitchen temperature

°C

Ready in about we will pick the ratio for you

Feeding ratio

A starter straight from the fridge is cold and acidic. Give it a big feed to dilute that acid, and expect to feed it twice before it is reliable again.

Ratio (starter : flour : water)

: :

Your feed

50g starter to keep

50g flour to add

50g water to add

Discard the rest of your starter before feeding, or save it for discard recipes like pancakes and crackers.

How to Use the Sourdough Calculator

The calculator has two modes. Feed My Starter works out a feeding by ratio, and Bread Dough builds a full recipe using baker’s percentages.

Feeding your starter

A feeding ratio is written as starter : flour : water. A 1:1:1 feed means equal weights of each, the everyday maintenance feed. A bigger ratio like 1:5:5 gives the starter far more food, so it rises more slowly and is perfect to feed once and leave overnight. Enter how much fed starter you want and the calculator tells you how much to keep, plus the flour and water to add.

Working out a dough

Bakers measure everything as a percentage of the flour, called baker’s percentage. Hydration is the water as a percentage of the flour, so 70% hydration means 700g of water for every 1000g of flour. Salt is usually around 2%. Because your starter is itself made of flour and water, the calculator subtracts what is already in it, so your finished dough lands at exactly the hydration you asked for.

What Hydration Should I Use?

60 to 65% - stiff and easy to shape, great for beginners and sandwich loaves.
68 to 72% - the classic all-round sourdough, open but still manageable.
75 to 80% - a wetter dough with bigger holes that needs a gentler hand.
80% and above - focaccia and ciabatta territory, very slack and sticky.

What You’ll Need for Sourdough

The right kit makes sourdough far less fiddly. These are the tools I actually use to bake at home.

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Digital Kitchen ScaleWeigh flour, water and starter in grams so the calculator’s numbers land exactly right. Banneton Proofing BasketSupports the dough as it proves and gives that classic floured, ringed crust. Cast-Iron Dutch OvenTraps steam for a dramatic rise and a crackly, bakery-style crust at home. Bread LameScore the top so the loaf opens up cleanly instead of bursting at the side. Bench ScraperHandles wet, high-hydration dough and makes dividing and shaping easy. Instant-Read ThermometerCheck dough and water temperature to keep fermentation on schedule. Starter JarA tall jar with a band to mark the rise, so you can see when your starter peaks. Strong Bread FlourHigh-protein flour that gives sourdough its chew, structure and open crumb. Danish Dough WhiskMixes shaggy, sticky dough in seconds without it clinging to your hands.

Sourdough in a Cold Kitchen

Nearly every sourdough recipe you will read online was written for a dough sitting at 24 to 27°C. A British kitchen in winter is nowhere near that, which is why the timings never seem to work.

There is proper measured data on this rather than guesswork. The Energy Follow-Up Survey put temperature loggers in 823 English homes for a year. The whole-dwelling average was 18.1°C in December and 18.3°C in January, and 26% of households kept the living room below 18°C. Three honest caveats: the kitchen itself was not measured, only living rooms, hallways and bedrooms; it covers England rather than the whole UK; and it was recorded before the energy crisis, so if anything it flatters us. A kitchen is usually the coldest room in the house and the heating is off overnight, which is exactly when your dough is working.

Here is what that does to a loaf. These figures come from a set of over sixty controlled test bakes.

Dough temperature	Bulk ferment	Target rise
27°C / 80°F	about 5.5 hours	25 to 35%
25°C / 77°F	about 6 hours	40%
23°C / 74°F	about 8 hours	55%
22°C / 72°F	about 10 hours	65%
21°C / 70°F	about 12 hours	75%
20°C / 68°F	about 14 hours	85%
19°C / 66°F	about 16 hours	95%
18°C / 65°F	16 hours or more	100% or more

Now the part that catches people out, because it runs the wrong way to intuition. The colder the dough, the further you let it rise before you shape it. The advice you see everywhere, bulk until it has risen 30 to 50%, is warm-dough advice. Follow it in a 19°C kitchen and you will stop the bulk less than half way and bake a dense loaf, then blame your starter.

The reasoning is straightforward once you see it. At 27°C the dough carries on fermenting hard through shaping, proving and the first minutes in the oven, so you hit the brakes early. At 19°C almost nothing happens after you shape it, so the bulk has to do all the work.

Two things to hold on to, or this will mislead you. Those target rises assume you are giving the shaped loaf a cold retard in the fridge afterwards, roughly 8 to 16 hours. Without one, stop a little earlier. And judging by percentage rise is a method with a proponent, not a universal law: plenty of very good bakers ignore the numbers entirely and go by how the dough feels and behaves.

Flour matters here too. Those figures assume a bread flour at around 12.5% protein. Plain flour sits at roughly 9 to 10% and simply will not hold that much gas, so it will never show you a 95% rise. Worth knowing that the spread within British flour is wider than any gap between countries: own-brand strong white runs from about 11% to nearly 15% depending on whose bag you pick up.

If your kitchen is warm, and most American kitchens are, read the table from the top instead. Your dough will be ready in a third of the time and you should be stopping at a 25 to 35% rise, not waiting for it to double.

And there is a consolation for the cold. A slow ferment at around 18°C gives a sharper, more sour loaf, because the bacteria carry on making acid while the yeast makes less gas. A cold kitchen is not purely a handicap, it is a different loaf. If your dough has stopped entirely rather than merely slowed, that is a different problem and I have written about it in why dough will not rise in a cold kitchen.

Sourdough Calculator FAQ

What is baker’s percentage?

It is a way of writing a recipe where every ingredient is shown as a percentage of the total flour, and the flour is always 100%. It makes a recipe easy to scale: keep the percentages the same and just change the flour weight.

How much starter should I use in my dough?

Most sourdough loaves use around 20% starter, which is 100g for every 500g of flour. More starter ferments the dough faster, less starter ferments it more slowly. The calculator lets you set any amount and adjusts the rest.

Does the calculator account for the flour and water in my starter?

Yes. In Bread Dough mode it works out how much flour and water your starter already holds, based on its hydration, and subtracts them. The flour and water it tells you to add give the exact hydration you set.

What feeding ratio is best?

For daily upkeep at room temperature, 1:1:1 is fine. If you want to feed once and leave it overnight, use a larger ratio like 1:3:3 or 1:5:5 so the starter does not run out of food and collapse before you get to it.

How do I revive a starter from the fridge?

Take it out, discard most of it, and feed it a couple of times at room temperature until it doubles reliably. The Revive from fridge preset uses a gentle 2:1:1 feed to wake it up. My sourdough starter guide walks through the whole process.