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Sourdough Starter Calculator: Get Your Ratios Right

Your feeding ratio is the single number that controls whether your starter thrives or slowly dies. It's the proportion of existing starter to fresh flour to fresh water — written as something like 1:2:2 or 1:5:5 — and once you understand what it means, you stop guessing and start baking on purpose. I spent two years feeding my starter the same way every single day before I realized I was the problem. A calculator changes that fast.

What That Ratio Actually Means (It's Simpler Than It Looks)

A feeding ratio like 1:1:1 means equal parts starter, flour, and water by weight. So 20g of starter gets 20g of flour and 20g of water. That's it. The first number is always your existing starter — sometimes called the "inoculation" — and the second and third numbers are your fresh flour and water.

Most recipes you'll see online use 1:1:1 as a default. It's fine for daily baking at room temperature. But it's not a universal truth. It's just a starting point, and knowing how to adjust it is where things get interesting.

The ratio controls how fast your starter peaks. A small starter amount relative to a large flour dose (say, 1:5:5) means slower fermentation — your wild yeast has more food and takes longer to work through it. A higher inoculation like 1:1:1 peaks faster, sometimes in just 4 hours at 76°F.

When to Feed 1:1:1 and When to Go Higher

Feed 1:1:1 when you bake every day. Your starter moves fast at this ratio — expect peak activity in 4 to 6 hours at room temperature (68–72°F). It's the workhorse ratio, and it keeps things simple when you're in a regular baking rhythm.

Go to 1:2:2 or 1:3:3 when your schedule is unpredictable. More food means a longer, slower rise — often 8 to 12 hours — which gives you a bigger window to catch your starter at peak. I use 1:3:3 every Friday night so my starter is ready Saturday morning without me waking up at 5 a.m.

A 1:5:5 or even 1:10:10 ratio is for bakers who only bake once or twice a week. At these high ratios, a starter can take 12 to 16 hours to peak at 70°F, which is perfect for overnight fermentation. The tradeoff is that a heavily diluted starter takes longer to build strength after neglect — so don't jump straight to 1:10:10 with a young starter.

How a Calculator Actually Runs the Math

Here's where the tool earns its place. You tell our sourdough starter feeding calculator three things: how much starter you want to end up with, what ratio you're targeting, and what hydration you're working at. It does the rest.

Say you want 150g of starter at 1:2:2 hydration. The calculator works backward: you need 30g of existing starter, 60g of flour, and 60g of water. That's (30 + 60 + 60 = 150g). Doing this by hand with any ratio that isn't a round number gets tedious fast. A 1:3.5:3.5 ratio at 75% hydration? Nobody wants to do that arithmetic at 7 a.m.

Hydration matters here too. A 100% hydration starter (equal flour and water by weight) is standard for most home bakers. But if you're running a stiffer starter at 65% hydration — common in Italian panettone traditions — your water weight drops and your flour weight rises proportionally. The calculator adjusts for this automatically.

The Temperature Factor Nobody Tells You About

Your kitchen temperature changes everything. A starter fed at 1:2:2 peaks in 8 hours at 68°F. That same ratio peaks in 4 hours at 80°F. Same starter, same ratio, wildly different timeline.

This is why "feed it twice a day" is such imprecise advice. Twice a day works at 72°F. It's too often at 65°F in winter — your starter never fully depletes before you feed again, which builds acidity and weakens the culture over time. In summer at 80°F, twice a day might not even be enough.

The fix is watching your starter, not your clock. Learn what peak looks like for yours — typically doubled in volume, domed top, active bubbles throughout — and feed based on that. The calculator helps you choose a ratio that makes peak timing predictable given your actual kitchen temperature.

How to Calculate the Right Amount of Starter for a Recipe

Most sourdough bread recipes call for somewhere between 15% and 25% starter as a percentage of the total flour weight. That's called the inoculation rate, and it's the ratio that actually controls fermentation speed in your dough — not just your feeding schedule.

If a recipe uses 500g of flour and calls for 20% starter, you need 100g. Simple. But you also need to make sure that 100g of starter is at the right hydration for the recipe. If your starter is 100% hydration and you're adding 100g of it, you're adding 50g of flour and 50g of water into your dough — that affects your total dough hydration. Serious bakers account for this. Our sourdough starter feeding calculator makes this adjustment automatic.

Where new bakers get into trouble: pulling starter straight from the fridge, cold and sluggish, and expecting it to leaven a loaf properly. Always feed your starter at least once — ideally twice — before using it in a recipe. Feed it, let it peak, use it at peak. That's the rule.

Signs Your Ratio Is Off (And How to Fix It)

A starter that smells aggressively sour — like nail polish remover or very sharp vinegar — is over-acidified. It's eating through its food too fast and sitting in its own waste products. The fix is a higher ratio (more food relative to starter) to dilute that acidity and give the yeast more runway. Try jumping to 1:4:4 for a few days.

A starter that barely rises, looks flat after 12 hours, and smells weakly yeasty is under-fed or overly diluted. Too high a ratio for a young or struggling culture means the yeast population can't work through all that flour efficiently. Drop down to 1:1:1 and feed twice daily until you see consistent doubling within 6 to 8 hours at room temperature.

If you're seeing separation — a gray liquid layer on top — that's "hooch," and it means your starter went way past peak and is starving. It's not dead. Pour off the hooch, discard all but 10g of starter, and feed at 1:2:2 twice a day for three days. You'll bring it back. I have a full breakdown of these scenarios in our sourdough starter troubleshooter if you need a deeper diagnosis.

Building a Feeding Schedule That Actually Works for Your Life

The best feeding schedule is the one you can stick to. That sounds obvious. But I've watched dozens of bakers adopt some rigorous twice-daily regimen for a week, burn out, and abandon their starter in the fridge for three months.

If you bake once a week, keep your starter in the fridge and feed it once weekly. Pull it out the night before baking, feed at 1:2:2, let it peak at room temperature, and use it. That's a sustainable system for most home bakers and it works beautifully.

If you bake several times a week, a counter starter fed daily at 1:2:2 makes more sense. You always have active starter ready, and the daily feeding becomes as automatic as making coffee. Adjust the ratio based on your kitchen temperature as the seasons change — up in summer, down in winter.

Write your ratio down somewhere. Literally tape a sticky note to your jar. You'll thank yourself at 6 a.m. when you're half-asleep and trying to remember if it was 1:2:2 or 1:3:3 last time.

Frequently Asked Questions

What's the best feeding ratio for a beginner?

Start with 1:1:1 — equal parts starter, flour, and water by weight. It's predictable, easy to calculate, and gives you clear feedback on your starter's activity. Once you understand how your starter behaves at this ratio, you'll have a baseline to compare against when you scale up or down. Most kitchens at 68–74°F will see peak activity 5 to 8 hours after a 1:1:1 feeding.

Can I use volume measurements instead of weight?

You can, but you'll get inconsistent results. Flour especially is notoriously variable by volume — a cup of bread flour can weigh anywhere from 120g to 160g depending on how it was scooped. A kitchen scale costs about $12 and changes everything. Weight is the only way to make ratios reproducible across different sessions, different flours, and different bakers.

How much starter should I keep on hand?

Keep only as much as you need, plus a small buffer. If a recipe calls for 100g of starter, maintain about 50g in your jar — feed it to produce 150g or so, use 100g for baking, and return 50g to maintain. Keeping massive quantities of starter means massive amounts of discard at every feeding, which is wasteful and unnecessary. Smaller jars, smaller amounts, same strong results.

Does the type of flour change the ratio I should use?

It changes the timing more than the ratio itself. Whole wheat and rye flours ferment significantly faster than white bread flour — rye especially, which can nearly double fermentation speed. If you switch from 100% bread flour to a blend with 20% rye, expect your starter to peak 2 to 4 hours earlier than usual. You might compensate by increasing your ratio slightly (more food) or by feeding at a cooler temperature to slow things down.

Ready to Stop Guessing and Start Baking?

Ratios make sourdough predictable. Not boring — predictable. There's a difference. Once you know your starter peaks at 1:2:2 in 9 hours at 70°F, you can plan your entire baking day around that single fact. Ready to start?