How does room temperature affect my starter?

Temperature is the biggest factor in fermentation speed. At 24°C a 1:5:5 feed might peak in about 9 hours, but at 18°C the same feed could take several hours longer. Each degree below 24°C slows fermentation by roughly 10%. Because a cool kitchen is already slower, this calculator suggests a lower feeding ratio (less flour and water) so the starter still peaks by your target time; in a warm kitchen it suggests a higher ratio. If your kitchen is very cool, you can also move the jar somewhere warmer like an airing cupboard or on top of the fridge.

What feeding ratio should I use?

The ratio depends on when you need the starter to peak (figures are for white flour at about 24°C). For a quick turnaround (~4 hours) use 1:1:1 (equal parts starter, flour, water). Around 7 hours use 1:3:3. For overnight (~9-13 hours) try 1:5:5 up to 1:10:10. Higher ratios mean more dilution and a longer, milder ferment. This calculator works backwards from your target time, temperature and flour type to suggest the right ratio.

Does flour type affect peak time?

Yes. Wholemeal and rye flours ferment faster than white flour because they contain more nutrients, enzymes and wild yeast. Rye is the fastest — a rye-fed starter can peak around 20% quicker than white at the same ratio. Spelt falls between white and wholemeal. Because these flours are faster, the calculator suggests a slightly higher feeding ratio (more dilution) so they still peak at your target time rather than racing ahead.

What hydration should my starter be?

100% hydration (equal weight flour and water) is the most common and easiest to manage. This creates a thick, pancake-batter consistency. Some bakers prefer a stiffer starter at 60-80% hydration for more complex flavours and slower fermentation. Liquid starters at 125%+ hydration are sometimes used for ciabatta and focaccia.

How do I know when my starter has peaked?

A peaked starter has doubled or tripled in volume, has a domed surface, and is full of bubbles. If the surface has started to sink or flatten, it has passed its peak. Use a rubber band around the jar at feed time to track the rise. The float test (a spoonful floats in water) also indicates peak readiness.

Sourdough Feeding Calculator — Free Bread & Dough Tool

How We Calculate This

This calculator determines the best feeding ratio for your sourdough starter based on when you need it to peak. It factors in room temperature and flour type.

How it works

Higher feeding ratios (more flour and water relative to starter) take longer to peak
Warmer temperatures speed up fermentation, so a cool kitchen needs a lower ratio to still peak on time; a warm kitchen needs a higher one
Wholemeal and rye flours ferment faster than white, so they need a slightly higher ratio for the same target time
The ratio is expressed as starter : flour : water

Rough timing guide at 24°C with white flour

1:1:1 — peaks in ~4 hours
1:2:2 — peaks in ~5-6 hours
1:3:3 — peaks in ~7 hours
1:5:5 — peaks in ~9 hours (good for overnight)
1:10:10 — peaks in ~13 hours (long overnight build)

Peak times are estimates only — starter strength, exact temperature and flour all shift the timing. Watch your starter and use the rise (it should roughly double or triple and dome) rather than the clock to judge when it has peaked.

Frequently Asked Questions

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Last updated: March 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.