Sourdough Calculator
Set the loaf weight, hydration, starter percentage and salt, and get exactly what to add, with the starter's own flour and water already accounted for. Then work out the feed that gets you enough ripe starter.
Loaf formula
900 g fills a 9-inch banneton; 1,000 g a 10-inch
Includes the flour and water in the starter
15-25% is typical; more is faster
100% = equal flour and water
Flour to add
458 g
Water to add
331 g
Starter
102 g
51 g flour + 51 g water
Salt
10.2 g
Total flour = 900 ÷ (1 + 75% + 2%) = 508 g, of which 51 g arrives in the starter. Total water = 381 g, of which 51 g is in the starter. The levain is 11.3% of the dough by weight.
Starter feeding
How much to feed so you have enough ripe starter for the loaf, plus some to keep.
Mature starter
40 g
Flour
40 g
Water
40 g
Ready in about
4 h
at 75°F, 1:1:1
Build = 100 + 20 = 120 g, split into 3 parts. Higher flour-to-starter ratios (1:5:5, 1:10:10) peak later and taste milder; 1:1:1 peaks in about four hours and is more sour.
The arithmetic, once
Everything is a share of total flour, and total flour includes the flour inside the starter. For a 900 g loaf at 75% hydration and 2% salt, dough = flour × (1 + 0.75 + 0.02), so flour = 900 ÷ 1.77 = 508 g and water = 381 g. A 20% starter is 102 g; at 100% hydration that is 51 g flour and 51 g water, which you subtract: add 458 g flour, 331 g water, 10 g salt.
A 900 g loaf at every common hydration
| Hydration | Add flour | Add water | Starter (20%) | Salt (2%) | Feel |
|---|---|---|---|---|---|
| 65% | 485 g | 296 g | 108 g | 10.8 g | Firm, easy to shape, tight crumb |
| 70% | 471 g | 314 g | 105 g | 10.5 g | Beginner-friendly, moderate crumb |
| 75% | 458 g | 331 g | 102 g | 10.2 g | The standard country loaf |
| 80% | 445 g | 346 g | 99 g | 9.9 g | Slack, open crumb, needs strong flour |
| 85% | 433 g | 361 g | 96 g | 9.6 g | Very wet; coil folds, not kneading |
Feeding ratios and when the starter peaks
| Ratio | For 120 g build | Peaks in (75°F) | Character |
|---|---|---|---|
| 1:1:1 | 40 + 40 + 40 g | ~4 h | Fast, tangy; feed twice a day |
| 1:2:2 | 24 + 48 + 48 g | ~6 h | Everyday maintenance |
| 1:5:5 | 11 + 55 + 55 g | ~9 h | Overnight build, mild |
| 1:10:10 | 6 + 57 + 57 g | ~12 h | Long build, very mild; hot kitchens |
Use the starter at or just before its peak, when it has doubled or more and the surface is domed. A spoonful that floats in water is the usual test. Past the peak it collapses and turns acidic, which still leavens but with less lift.
Frequently Asked Questions
How do I calculate sourdough hydration when the starter has water in it?
Count the starter's flour and water as part of the totals. A 100%-hydration starter is half flour, half water. For a 900 g loaf at 75% hydration, 20% starter and 2% salt: total flour = 900 ÷ 1.77 = 508 g, starter = 102 g (51 g flour + 51 g water), so you add 458 g flour and 330 g water. Recipes that ignore the starter's water end up 3-5 points wetter than they say.
What hydration should a sourdough loaf be?
70-75% is the comfortable range for a beginner with bread flour: open enough crumb, still shapeable. 78-85% gives the very open crumb in photos but needs strong flour and confident shaping. Whole wheat and rye absorb more water, so add 5-10 points when they are a large share of the flour. Under 65% makes a tight, sandwich-style loaf.
How much starter should I use?
Between 15 and 25% of the flour weight is standard: 20% for a bulk ferment of 4-6 hours at 75°F. Use 10% for an overnight bulk in a cool kitchen or a milder flavour; 30-40% to hurry a summer bake. More starter is faster and, past a point, more sour and weaker in structure.
What does a 1:5:5 feeding ratio mean?
One part mature starter, five parts flour, five parts water, by weight. 10 g starter + 50 g flour + 50 g water makes 110 g. Higher ratios take longer to peak (8-12 hours for 1:5:5 versus 4 hours for 1:1:1) and give a milder, less acidic levain. The feeding calculator works out the three amounts from what you need for the loaf plus what you keep back.
How much salt goes in sourdough?
2% of the total flour weight, including the starter's flour: 10 g for 500 g flour. 1.8% is noticeably mild; 2.2% is the upper end for a table loaf. Salt tightens gluten and slows fermentation slightly, which is why some bakers add it after a 30-minute autolyse.
These tools use baker's percentages, salt-by-weight brining, coffee ratios by weight and the USDA roasting and thawing tables, all stated on each page. They are starting points for your kitchen, your flour and your oven: taste the brine, watch the dough, and always cook poultry to 165°F on a thermometer.