What is baker's math? A plain-English guide to baker's percentages

The core idea: flour is always 100%

Here's the whole thing in one sentence. In baker's math, every ingredient is expressed as a percentage of the flour weight. Flour is always 100%. Everything else is measured against it. That's it.

So if your recipe uses 500g of flour and 375g of water, your water is 75% (375 ÷ 500 × 100). Salt at 10g is 2%. A 100g sourdough starter is 20%. You're just asking: for every 100g of flour, how much of this ingredient am I using?

One thing that trips people up: the numbers don't add up to 100. A typical sourdough loaf with 100% flour, 75% water, 20% starter, and 2% salt adds up to 197%. That's completely normal. These aren't slices of a pie. They're ratios, all anchored to the same thing: your flour.

Why bakers use percentages instead of grams

You might be wondering why anyone bothers with this instead of just writing the recipe in grams. Fair question. The answer is scaling, and once you feel the difference, you'll get it immediately.

Say your recipe makes one loaf and you want to make three. In grams, you go through every ingredient and multiply by three. Fine. But what if you want exactly 900g of dough to fit your banneton, or 14 rolls instead of 8? Now you're solving a maths problem before you even get to bake anything.

With baker's percentages, you just change the flour weight. Everything else follows automatically. The percentages never change. Want a 900g loaf? Work backwards to find the flour, multiply each percentage, done in 30 seconds. The recipe is the same recipe at any size.

This is how every professional bakery operates. The same formula that works for your weekend loaf runs their entire production. Once you bake this way a few times, going back to fixed gram recipes feels like tying one hand behind your back.

How to calculate baker's percentages

Let's do the maths so you can see exactly how it works. Going from grams to a percentage: divide the ingredient by the flour weight and multiply by 100.

Going the other way, from a percentage back to grams: divide the percentage by 100 and multiply by your flour weight.

There's one more trick worth knowing. If you know the total dough weight you want but need to figure out the flour, use the sum of all percentages to work backwards.

Using the sourdough example: total dough 985g, percentages add up to 197%. So flour = 985 ÷ 1.97 = 500g. Then every other ingredient falls out from that. That's exactly what the calculators on this site do. Tell them how much dough you want and they handle the rest.

Hydration: the number that tells you everything

Out of all the baker's percentages, hydration is the one you'll use most. It's simply the percentage of water in your dough. And it tells you almost everything about what you're about to make.

A bagel dough sits at 55–60%. Dense, stiff, holds its shape perfectly for boiling. A classic sourdough loaf is usually 70–75%. A ciabatta or focaccia can push 80–90%. At that point you're almost pouring the dough into the tin.

Once hydration clicks for you, reading a recipe changes completely. You see “85% hydration” and you already know: this dough will be wet and sticky, work it in the bowl not on the bench, expect a very open crumb. You know all that before you've touched a single gram of flour.

Numbers worth memorising

After a few bakes with this system, a handful of numbers will start to stick. Salt almost always lives between 1.8% and 2.2%. That range is where you get full flavour without slowing the yeast down. Go below 1.5% and the bread tastes thin. Go above 2.5% and fermentation drags.

Sourdough starter typically runs 15–25% for a same-day or overnight bake. Less starter means slower fermentation, which is great for cold retards and long schedules. More starter wakes things up, which helps when your kitchen is cool. If you use instant yeast, you need far less than most supermarket recipes tell you. A same-day bake usually only needs 0.5–1%.

Fat and sugar percentages are where things get really interesting. A lean baguette is 0% fat. A brioche can be 50% butter and 20% sugar. Both are bread. Baker's math lets you see exactly where any recipe sits on that spectrum and understand why it behaves the way it does.

The sourdough wrinkle most recipes get wrong

Here's something that surprises most sourdough bakers the first time they hear it. Your starter is not just an ingredient. It's flour and water. A 100% hydration starter, fed equal weights of each, contributes half its weight as flour and half as water to your dough.

Most recipes ignore this completely. They list the starter as an ingredient and calculate hydration against the main flour only. So when a recipe says “75% hydration”, it's actually an estimate. Sometimes a rough one.

Here's the real maths. A recipe with 500g flour, 100g of 100% hydration starter (that's 50g flour + 50g water), and 375g added water has a true total flour of 550g and true total water of 425g. Real hydration: 425 ÷ 550 = 77.3%, not 75%. Over many bakes, that 2% gap compounds. The sourdough hydration calculator accounts for this automatically so you always hit your actual target.

How to make it click for yourself

The best way to get this into your hands is to take a recipe you've already baked. One you know well. Convert every ingredient to a baker's percentage by dividing by the flour weight. Write them down. Then bake it again using those percentages as the recipe. After one or two bakes, the numbers start feeling natural.

From that point, reading new recipes is a different experience. You see “72% hydration, 2% salt, 18% starter” and you already know the dough before you make it. Manageable, not too wet, moderate starter, probably 4–5 hours at room temperature. You stop following recipes blindly and start understanding them.

All the calculators here are built on baker's percentages. Give them your flour weight and target percentages and they hand you exact grams. Or go the other way: enter your gram amounts and see the percentages they represent. Use whichever direction you need.

References

1. King Arthur Baking Company. Baker's Percentage: The Math Behind the Recipe. kingarthurbaking.com
2. Hamelman, J. Bread: A Baker's Book of Techniques and Recipes. 2nd ed. John Wiley & Sons, 2012. The standard professional reference for baker's percentages in production baking.
3. Robertson, C. Tartine Bread. Chronicle Books, 2010. Brought high-hydration sourdough percentages to home bakers.
4. The Fresh Loaf. Baker's Math and Percentages, Community Guide. thefreshloaf.com
5. Suas, M. Advanced Bread and Pastry. Cengage Learning, 2008. Covers baker's percentage systems used in professional pastry and bread production.