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Sourdough calculator

Sourdough Starter Feeding Calculator

Pick a feeding ratio and how much starter you need, and see exactly what to keep, discard and feed.

A jar of bubbly sourdough starter
Plan the feed
g
g

Ripe starter for your recipe, plus a little left in the jar for the next feeding.

Ratio starter : flour : water

The Perfect Loaf feeds 1:5:5 twice a day, every 12 hours, in a 75–78 °F kitchen.

× starter
× starter
Starter details100%
%
g

Hydration is the water per 100 g of flour in your starter now; 100% means equal flour and water. Weigh what is in your jar (without the jar) to see how much to discard.

Your feed

Makes 220 g (7.8 oz) of starter: 200 g for your recipe and 20 g to keep.

Ratio
1:5:5S : F : W
Fed starter
220 g7.8 oz
Hydration
100%after feeding

What the fed starter is made of, by weight.

  • Ripe starter20%keep this much, discard the rest · ≈ 1 1/4 tbsp20 g0.71 oz
  • Flour100%all-purpose, bread or part whole grain · ≈ 3/4 cup + 1 tbsp100 g3.5 oz
  • Water100%lukewarm · ≈ 1/4 cup + 3 tbsp100 g3.5 oz

Add the weight of your starter jar contents under "Starter details" to see how much to discard.

The feed in baker's percentages
IngredientWeightBaker's %
Fresh flour100 g100%
Fresh water100 g100%
Ripe starter20 g20%

Percentages are of the fresh flour. Times to peak are what each source reported for its own starter, not a prediction for yours. Cups and spoons are approximate, based on King Arthur Baking's ingredient weights (all-purpose flour, 120 g per cup); a kitchen scale gives the best results.

How it works

A feeding ratio is written starter : flour : water by weight, so a 1:5:5 feed has 11 equal parts. The calculator adds up the starter you want to end with, divides it into parts, and gives one part to the old starter:

starter to keep = (starter needed + leftover) ÷ (1 + flour parts + water parts)

flour = starter to keep × flour parts, water = starter to keep × water parts

In "Just feeding" mode you enter the starter you keep and it simply multiplies. The hydration after feeding counts the flour and water already in the old starter, which is split as flour = starter ÷ (1 + hydration).

Worked example

  1. You need 200 g of ripe starter for a recipe and want 20 g left over: 220 g in all, fed 1:5:5.
  2. 1 + 5 + 5 = 11 parts, so one part is 220 ÷ 11 = 20 g of starter to keep.
  3. Flour = 20 × 5 = 100 g. Water = 20 × 5 = 100 g.
  4. Check: 20 + 100 + 100 = 220 g. Hydration = (10 + 100) ÷ (10 + 100) = 100%.

These numbers are Maurizio Leo's own routine from The Perfect Loaf: 20 g of ripe starter with 100 g of flour (70 g white, 30 g whole rye) and 100 g of water, fed every 12 hours in a 75–78 °F kitchen. The times to peak under the other ratios come from King Arthur Baking's 2025 feeding-ratio trial at 78 °F. Brød & Taylor's tests point the same way: 1:1:1 ripened in 4 to 5 hours, 1:8:8 needed about 10.

FAQ

What does a 1:5:5 feeding ratio mean?

It is starter : flour : water by weight. Keep 1 part ripe starter and add 5 parts flour and 5 parts water, so 20 g of starter gets 100 g of flour and 100 g of water. That is the feed Maurizio Leo of The Perfect Loaf gives his starter twice a day.

Which feeding ratio should I use?

Pick the one that peaks when you need it. In King Arthur Baking's trial at 78 °F, a 1:1:1 starter doubled in about 4 hours, 1:2:2 peaked after 8 hours and 1:4:4 after 12. A cool kitchen slows all of them, so use a smaller ratio there and a larger one when it is warm. King Arthur also found that the ratio made no difference to how the starter performed in the bread.

How much starter should I discard?

Everything except the ripe starter you keep for the feed. Enter what is in your jar under "Starter details" and the calculator shows the discard. You can bake with the discard instead of throwing it away.

Does the feeding ratio change my starter’s hydration?

Only if the flour and water parts differ. Equal parts keep a 100% starter at 100%. A 1:5:2.5 feed builds a stiff starter of about 55%, because only half as much water as flour goes in. The calculator shows the fed starter’s hydration, counting the flour and water already in the old starter.

How much starter do I need for one loaf?

Check your recipe. The Perfect Loaf's beginner's sourdough uses about 95 g of levain per loaf, and our sourdough calculator works it out for any loaf. Plan a little extra to keep back for the next feeding.

Sources