Sourdough Starter Feeding Calculator: Ratios to Grams

How the math works

A ratio of 1:r:r means for every gram of starter (the seed), add r grams of flour and r grams of water. The total after feeding is 1 + r + r = 1 + 2r parts. So to end up with T grams:

• Seed = T ÷ (1 + 2r)
• Flour = water = seed × r

For 180 g at 1:2:2: seed = 180 ÷ 5 = 36 g; flour and water = 72 g each.

Since flour and water are equal in all of these, they all make a 100% hydration starter.

Ratio and timing

The more food you give relative to the seed, the longer the starter takes to eat through it and peak. In King Arthur Baking's published trial at 78°F, aiming for 180 g of starter:

• 1:1:1 doubled and was ready at 4 hours, starting to fall by 8 hours, and ready to feed again at 12.
• 1:2:2 was nearly doubled at 4 hours and peaked at 8.
• 1:4:4 had not doubled at 4 hours, was nearly doubled at 8, and peaked at 12.

The author notes every starter is different; cooler kitchens slow everything down. The same article says larger ratios such as 1:8:8 or 1:10:10 can stretch maintenance to about once a day.

Planning around your bake

Work backward from when you want to mix the dough:

• Mixing in the afternoon? Feed 1:1:1 in the morning.
• Mixing first thing in the morning? Feed 1:4:4 or so before bed.
• Out all day? Try a larger ratio in the morning and check it in the evening.

Watch the starter rather than the clock: at peak it has roughly doubled, with bubbles throughout and a domed or just-flattening top.

Maintenance feeding

King Arthur Baking's maintenance routine keeps 113 g of starter and feeds it 113 g each of flour and water: every 12 hours at room temperature, or about once a week from the refrigerator (letting it bubble on the counter for 1 to 2 hours before chilling). Its guide notes that feeding times are flexible: a few hours early or late is fine.

More in our starter feeding guide.

Weigh, don't scoop

Feeding ratios are by weight. A cup of flour and a cup of water weigh very different amounts, so volume measures distort the ratio. A kitchen scale that reads in single grams is the easiest way to feed accurately.

Common questions

How much starter, flour and water for 180 g at 1:2:2?

36 g starter, 72 g flour and 72 g water. That matches the amounts King Arthur Baking used in its feeding ratio trial.

Which ratio should I use?

Pick by timing. A 1:1:1 feed peaks soonest, useful when you'll bake the same day. A 1:4:4 feed before bed can be ready the next morning. Feeding ratio doesn't change how the starter performs in the bread, only when it peaks.

What is the minimum I should feed?

King Arthur Baking says a starter should be fed at least a 1:1:1 ratio so the culture stays healthy and balanced.

Can I keep some back for next time?

Yes. Enter the amount to keep in 'Extra to keep back' and the calculator scales the feed so you have enough for both.