Sourdough Calculator

What is a sourdough starter?

A sourdough starter is a jar of flour and water that is full of wild yeast and bacteria. It is what makes sourdough bread rise, in place of the packet of yeast other breads use. It also gives the bread its tangy taste.

Wild yeast is the yeast that lives naturally on flour and in the air around you. A starter catches it and keeps it growing, so you never buy a packet.

A starter is alive, so you keep it going by feeding it. You stir in fresh flour and water, and over the next several hours it bubbles, rises, and grows. When it is at its bubbliest, you scoop some into your bread dough. The rest stays in the jar for next time.

You can make a starter from just flour and water by feeding it every day until it bubbles and rises reliably, or get a spoonful from a friend who bakes. This calculator assumes yours is fed equal weights of flour and water.

The hidden water in your starter

A recipe that says “500 g flour, 350 g water” looks like a 70% dough. Add starter and that stops being true. A starter fed equal weights of flour and water is half of each, so every spoonful slips extra water and flour into the bowl.

The more starter a recipe uses, the wetter the dough really is. Here is the same 500 g flour and 350 g water with more and more starter:

That is why two recipes with the same “hydration” can feel so different in your hands. This calculator always counts the starter, so the number you type is the number your dough ends up with.

Sourdough recipe formula, with an example

Baker’s math, also called baker’s percentages, is a way to write a recipe as percents of the flour’s weight instead of cups or loose grams. Because every ingredient is tied to the flour, you can scale the whole recipe up or down by changing one number.

Here is how it works. Pretend your flour weighs 100, and measure everything else against it:

• 75% water means 75 g of water for every 100 g of flour.
• 2% salt means 2 g of salt for every 100 g of flour.
• 20% starter means 20 g of starter for every 100 g of flour you add from the bag.

Sourdough adds one twist. Your starter is made of flour and water too, so the calculator counts what is inside it when it works out the water and salt. You just enter the percents, and it handles that part.

Starting from loaves, the math runs backward from the dough you want:

Total dough = number of loaves x dough per loaf
Total flour = total dough / (1 + hydration + salt)
Flour to mix = total flour / (1 + starter % / 2)
Starter = flour to mix x starter %
Water to add = total flour x hydration - starter / 2
Salt = total flour x salt %

Starting from a flour weight skips the first two lines.

Say you want two 900 g loaves at 75% hydration, with 20% starter and 2% salt.

2 x 900 = 1,800 g dough
1,800 / 1.77 = 1,016.9 g total flour
1,016.9 / 1.10 = 924.5 g flour to mix
924.5 x 0.20 = 184.9 g starter

The dough needs 762.7 g of water in all. The starter already carries 92.4 g of it, so 670.3 g goes in from the tap. Salt is 2% of 1,016.9 g, or 20.3 g.

Turn your favorite recipe into percentages

Got a recipe you already love? Turn it into percentages once, and the calculator can scale it to any loaf size.

Say the recipe uses 1,000 g flour, 720 g water, 200 g starter, and 20 g salt. Split the starter in half, then divide by the total flour:

Total flour = 1,000 + 100 = 1,100 g
Total water = 720 + 100 = 820 g
Hydration = 820 / 1,100 = 74.5%
Starter = 200 / 1,000 = 20%
Salt = 20 / 1,100 = 1.8%

Enter 74.5, 20, and 1.8, then ask for one 900 g loaf. You get 464 g flour, 334 g water, 93 g starter, and 9.2 g salt: the same dough, just smaller.

Water to add at each hydration

This chart is for 500 g of flour and 100 g of starter, which makes 550 g of flour in all.

The hydration percent decides how the dough feels. At a low hydration like 65%, there is less water for the same flour, so the dough is firmer, holds its shape, and is easier to handle. At a high hydration like 80% or 85%, there is more water, so the dough is wetter and stickier and needs gentler shaping. Whole grain flour soaks up more water than white flour, so whole wheat doughs often use the higher hydrations in this chart.

New to sourdough? Start at 65% or 70%, bake a few loaves, then raise the hydration a little at a time.

Build just enough starter

The calculator tells you how much starter the dough needs, then how to feed for exactly that amount. A feeding ratio is starter to flour to water, by weight.

Each cell is starter + flour + water.

Why the ratio matters. After you feed a starter, it bubbles and rises until it peaks, then slowly sinks. It is strongest around that peak, so that is the best time to mix it into your dough. The ratio decides how long it takes to get there:

• 1:1:1 has a lot of starter and only a little new flour to eat, so it peaks soonest. Pick it when you want to mix your dough later the same day.
• 1:2:2 takes a bit longer. It is a good middle ground.
• 1:5:5 starts from a spoonful of starter and a lot of new flour, so it takes the longest. Pick it when you need more time, like feeding before bed and mixing in the morning.

Feeding extra is a different thing. It does not change the timing. It just makes more starter than the dough needs, so some is left in the jar to keep going for your next bake.

The same baker’s math works for pizza. The pizza dough calculator scales yeasted dough balls, and the recipe cost calculator prices a batch once you know your gram weights. You can also browse every Cooking & Kitchen calculator.

Limitations

The calculator assumes a starter fed equal weights of flour and water. Some bakers keep a stiff starter instead. That is a starter fed less water than flour, such as 50 g of water for every 100 g of flour, so it feels like a firm dough rather than a thick batter. Because it holds less water, your dough will come out a little drier than the hydration you enter.

Salt is figured on total flour, starter included. Some recipes base salt on the mixed flour only, which gives slightly less salt.

Weights are rounded to the gram, and salt to a tenth of a gram, so the parts may not add up to the exact total. The calculator also cannot judge your flour, your kitchen’s temperature, or how strong your starter is, and those decide how long the dough needs to rise.

Sources

• Culinary Math, Chapter 10: Baker's Percent (Open Washington)

Frequently asked questions