Sourdough hydration calculator
A hundred grams of 100% hydration starter is fifty grams of flour and fifty of water. Most hydration calculators ignore this, so a dough built on 500 g of flour with 20% starter really holds 550 g of flour, and 75% hydration means 413 g of water rather than 375. Pour the 375 on top of the starter instead and the dough lands nearer 77%. At low starter percentages the difference is small; at 30% or more it is enough to change how the dough handles.
Baker's percentages state every ingredient against the total flour weight, and a starter is part of that flour. Weigh 500 g of flour with 20% starter at 100% hydration and the dough holds 550 g of flour, so 75% hydration is 413 g of water. The starter already brings 50 g of that, leaving 363 g to pour in.
How to build a sourdough
Baker’s percentage puts flour at 100 and states everything else against it, which is what lets one notation describe a loaf at any size. It also means the numbers add up past a hundred: flour 100, water 75, salt 2, so the finished dough is 177 per cent of the flour weight. The 500 g build above ends at 973.5 g for that reason, and knowing the total before you start is the quickest way to find out that your dough will not fit the banneton you own.
The part almost every calculator drops is that the starter is flour and water rather than a separate ingredient. A starter kept at 100 per cent hydration holds equal weights of the two, so it is half flour by mass, and the "100 per cent" refers to water against the starter’s own flour rather than against the starter as a whole. Take 500 g of flour with 20 per cent starter and you have 100 g of starter carrying 50 g of flour and 50 g of water. The dough therefore contains 550 g of flour, not 500, so 75 per cent hydration means 412.5 g of water in total, of which the starter has already supplied 50. Pour 375 g on top of the starter instead, as a naive calculation suggests, and you have made a 77 per cent dough while believing it is 75.
Starter hydration changes that split and the tool follows it. At 100 per cent a starter divides evenly. A stiff starter at 50 per cent hydration is two parts flour to one part water, so 100 g of it brings 67 g of flour and 33 g of water. A liquid levain at 125 per cent brings 44 g and 56 g. Salt shifts with the same arithmetic, since 2 per cent of 550 g is 11 g rather than 10, and at 30 per cent starter the gap widens further.
What hydration actually buys you is handling and crumb, in that order. Below about 65 per cent the dough is stiff, the crumb is tight and close, and the whole thing is easy to shape. Around 75 it becomes workable and genuinely open. Past 80 it turns slack, wants coil folds rather than kneading, and repays a banneton and a properly hot Dutch oven. None of those is better than the others: a bagel is deliberately near 55 and a ciabatta near 85. The number tells you what technique the dough will demand before you have touched it. One caveat: it says nothing about your flour. Wholemeal and rye drink far more water than white, so a 75 per cent wholemeal dough handles like a 65 per cent white one and needs to be judged by feel rather than by the figure.
What people use it for
- Building a loaf from a target hydration rather than a fixed recipe
- Converting a recipe written for a different starter hydration
- Scaling a formula up or down by flour weight
- Reading a recipe stated purely in percentages
- Checking whether a dough will fit the banneton or tin you own
- Working out why a dough that should be 75 per cent handles like 80
Questions
Every ingredient stated as a percentage of the total flour weight, with flour itself at 100. The percentages add up well past a hundred, which is normal and not an error.
Because the percentage is water against the starter’s own flour, not against the starter. Equal weights of each means the starter is half flour and half water by mass.
It has to, and this counts it. Its flour joins the total flour and its water joins the total water, which is why 500 g of flour at 20 per cent starter gives a 550 g flour figure.
You build a wetter dough than you intended. Pouring 375 g of water onto a 20 per cent starter build lands you at roughly 77 per cent instead of 75, and the gap grows with the starter percentage.
Set the starter hydration field to its real figure. At 50 per cent, 100 g of starter is 67 g of flour and 33 g of water; at 125 per cent it is 44 and 56.
70 to 75 per cent for a first sourdough, 80 and above once a slack dough does not alarm you. Bagels sit near 55 and ciabatta near 85.
Two per cent of the total flour, which is 11 g here rather than the 10 you would get from the flour you weighed. Below about 1.5 per cent the dough slackens and the flavour flattens; above 2.5 it noticeably slows fermentation.
Ten to twenty per cent for a slow overnight rise, thirty or more when you want it done the same day. Less starter means more time, and more time usually means more flavour.
Yes, but temperature moves it more. The same dough is a different loaf at 20 °C and at 26, and adjusting the starter percentage is the coarser of the two levers.
Most likely the flour. Wholemeal, rye and spelt absorb considerably more water than white bread flour, so the same percentage produces a much stiffer dough. Judge it by feel and hold a little water back to add later if you are unsure.