Ask two bakeries for the same bread formula and you will often get two documents that look nothing alike. One is in kilogrammes for a 300 kg mix. The other is in grammes for a bench trial. Neither can be compared with the other until both are written the same way, and the way the trade writes them is on flour.

The convention

In baker's percentage, total flour is always 100%. Every other ingredient is written as a percentage of that flour weight, not as a percentage of the whole dough. Water at 62% means 62 kg of water for every 100 kg of flour. It does not mean water is 62% of the dough.

This is why the percentages add up to more than 100, which surprises people the first time they see it. A simple bread might total 165%. That is not an error. It is the direct consequence of measuring everything against flour rather than against the batch.

Hydration is simply the water figure in this system. The Bread Bakers Guild of America writes it as water divided by total flour, which is worth stating plainly because hydration quoted on total dough weight is a different and much smaller number.

Why it survives

The convention persists because it makes three things easy that are otherwise tedious.

  • Comparison. Two formulas written on flour can be read side by side even if one was a 2 kg trial and the other a 400 kg production mix.
  • Scaling. Any batch size falls out of one division, shown below.
  • Diagnosis. When a dough behaves differently between sites, the percentages tell you quickly whether the formula changed or the process did.

The arithmetic that scales it

The useful identity runs backwards from the dough you want. Add up every baker's percentage in the formula, including the flour's own 100, then divide the target dough weight by that total.

The Guild states it directly: to calculate the total flour weight, divide the total dough weight by the total baker's percentage. Their worked example divides 16.300 kg of dough by 1.63 to give exactly 10.000 kg of flour.

Once you have the flour weight, every other ingredient is that flour weight multiplied by its own percentage. Nothing else is needed.

Where people get caught

More than one flour

When a formula uses white, wholemeal and rye together, those individual flours must themselves sum to 100%. Every non-flour ingredient is then calculated against the combined flour weight, never against one of the flours. Applying a salt percentage to only the white flour is a common and expensive slip.

Confusing dough weight with sold weight

Baker's percentage describes dough at the mixer. It says nothing about what comes out of the oven. Moisture leaves during proving and baking, so the dough you scale is always heavier than the loaf you sell. If you need a finished weight, you have to scale the dough up to allow for that loss, and the only reliable figure for it is the one measured on your own line.

A caution on borrowed numbers. Published loss figures are rarely comparable, because different sources measure across different stages. Some cover only the oven, others run from mixer to cooled loaf and bundle divider, proving, baking and cooling together. Measure your own before you trust anyone's.

Putting it to work

None of this requires a spreadsheet that somebody has to maintain. The calculation is a division and a set of multiplications, which is exactly why we built it as a free tool rather than writing a longer article about it.