Baker's percentage calculator
Every ingredient against the flour weight, which is what baker’s percentage means — and both readings of “hydration”, because the same dough has two different numbers and recipes use both. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
Everything is a percentage of the flour
That is the whole convention, and it is the bit that is almost never stated. In baker’s percentage the flour is 100% by definition, and every other ingredient is given as a percentage of the flour weight — not of the dough, not of the total.
So the numbers add up to far more than 100, and they are supposed to. A loaf at 70% hydration with 2% salt is 172% before you count anything else.
And “hydration” means two different things
70% hydration means 70 g of water per 100 g of flour. The same dough is 41% water by total weight. Both numbers describe the identical bread and both get written down as “hydration”.
The case that really catches people is a 100% hydration starter — equal weights of flour and water. Compute it the other way round and the same jar is 50%. If one recipe says 100% and another says 50% for what is visibly the same mixture, neither author is wrong and they are not disagreeing about anything except which denominator they used.
This page gives both, every time, so you can tell which one your recipe means.
Why bakers do it this way
Because it makes a formula independent of batch size. A recipe at 70% hydration and 2% salt is the same bread whether you start with 500 g of flour or fifty kilos, and scaling it is one multiplication rather than a set of ratios that all have to be recomputed.
It also makes two formulas comparable at a glance in a way that gram weights never are.