If you've spent any time baking sourdough, you've probably noticed that recipes vary wildly. One says to use 20% starter while another uses 15%. Some call for 75% hydration, others swear by 80%. The difference between a beautiful open crumb and a dense brick often comes down to understanding baker's percentages -- a system that takes the guesswork out of sourdough baking.
Baker's math (also called baker's percentages) is the professional standard used in commercial bakeries worldwide. It expresses every ingredient as a percentage of the flour weight. This system lets you scale recipes to any batch size while maintaining exact ratios that produce consistent results.
What is Baker's Percentage?
Baker's percentage is simple in concept but powerful in practice. Flour is always 100%, and every other ingredient is calculated as a percentage of that flour weight.
Here's how it works:
Basic formula: (Ingredient weight / Flour weight) x 100 = Baker's percentage
For example, if your recipe has 500 grams of flour and 350 grams of water:
- Flour: 500g = 100%
- Water: (350 / 500) x 100 = 70%
- Salt: (10 / 500) x 100 = 2%
This percentage-based system is why professional bakers talk in ratios rather than specific amounts. A 75% hydration dough with 2% salt produces the same result whether you're making one loaf or ten loaves -- the percentages stay constant.
Standard Sourdough Ratios Explained
A typical sourdough formula includes four main components, each with a standard range:
Flour: 100%
This is your baseline. Most sourdough uses bread flour (12-13% protein), though you can substitute up to 20% of the weight with whole wheat, spelt, or rye flour.
Water (Hydration): 70-85%
Hydration percentage affects your crumb structure more than any other factor. Here's what different hydration levels produce:
- 65-70% hydration: Dense, moist crumb. Good for beginners. Creates softer dough that's easier to handle. Typical shaping time: 20-30 minutes per loaf.
- 75-78% hydration: The sweet spot for most home bakers. Open, irregular crumb with some larger holes. Medium-difficulty shaping. This is where most classic sourdough recipes land.
- 80-85% hydration: High hydration. Creates an open, airy crumb with large, irregular holes. Wet, sticky dough requiring technique and confidence. Professional competition standard.
- 90%+ hydration: Very wet dough used for ciabatta and focaccia styles. Requires lamination techniques and significant experience.
For example, if you're making a 1000-gram loaf of bread at 75% hydration:
- Flour: 1000g
- Water: 750g
Starter (Inoculation): 15-25%
Your sourdough starter keeps the fermentation happening. The percentage determines fermentation speed:
- 15% starter (100g in a 500g dough): Slow fermentation, 12-16 hours bulk. Develops more flavor. Best for cold kitchen or if you want to bake the next day.
- 20% starter (100g in a 500g dough): Moderate fermentation, 8-12 hours bulk. Standard recipe timing. Most common approach.
- 25% starter (125g in a 500g dough): Fast fermentation, 4-8 hours bulk. Use if your kitchen is warm or you need to bake quickly.
Higher percentages speed up fermentation; lower percentages slow it down. This is critical for timing your bake around your schedule.
Salt: 1.8-2.2%
Salt strengthens gluten, slows fermentation slightly, and enhances flavor. Stay within 2-3 grams per 500 grams of flour.
- 1.8% salt: Mild salt flavor, slightly faster fermentation.
- 2% salt: Standard for most recipes. 10 grams in a 500-gram loaf.
- 2.2% salt: Pronounced salt flavor, slightly more fermentation control.
Calculating Actual Weights From Percentages
Once you understand percentages, calculating ingredient amounts is straightforward:
Formula: (Baker's percentage / 100) x Flour weight = Ingredient weight
Let's say you want to bake a single loaf with 500 grams of flour, using these percentages:
- Flour: 100% = 500g
- Water: 75% = (0.75 x 500) = 375g
- Starter: 20% = (0.20 x 500) = 100g
- Salt: 2% = (0.02 x 500) = 10g
Total dough weight: 500 + 375 + 100 + 10 = 985 grams
Scaling Recipes Up and Down
Baker's percentages make scaling effortless. Want to make two loaves instead of one? Just double the flour weight and recalculate everything else.
One Loaf Example (500g flour)
- Flour: 500g
- Water (75%): 375g
- Starter (20%): 100g
- Salt (2%): 10g
Two Loaves Example (1000g flour)
- Flour: 1000g
- Water (75%): 750g
- Starter (20%): 200g
- Salt (2%): 20g
The percentages stay identical. The results will be the same quality and crumb structure regardless of batch size.
Adjusting for Whole Grain Flour
Whole wheat, rye, and spelt absorb water differently than white flour. They require about 5-10% more water. If you're substituting 100 grams of your 500-gram flour with whole wheat:
- Regular percentages: 75% hydration = 375g water
- Adjusted for whole wheat: 75% + 7.5% (adjustment) = 82.5% = 412g water
This prevents dense, dry crumb when using whole grains.
Temperature and Fermentation Timing
Baker's percentages are fixed, but fermentation speed depends on temperature. Use these guidelines:
Cold (55-60F): 16-20 hour bulk fermentation. Best for developing complex flavor. Cool (60-65F): 12-16 hour bulk fermentation. Typical home kitchen temperature. Warm (70-75F): 8-12 hour bulk fermentation. Summer or warm kitchen. Hot (75F+): 4-8 hour bulk fermentation. Risk of over-fermentation.
At 70F, a 20% inoculation dough reaches proper fermentation in about 10-12 hours. At 55F, that same dough needs 18-20 hours. Same percentages, different timing.
Practical Example: Building Your Own Formula
Let's say you want a 1500-gram loaf with the following specifications:
- High hydration (80%) for open crumb
- Slow fermentation (15% starter) for flavor
- Standard salt (2%)
Calculate using percentages:
- Flour: 1500g รท 1.80 = 833g (flour weight calculation from total dough)
- Water (80%): 833 x 0.80 = 666g
- Starter (15%): 833 x 0.15 = 125g
- Salt (2%): 833 x 0.02 = 17g
Total: 833 + 666 + 125 + 17 = 1641g (close to 1500g; adjust flour to 800g if you want exactly 1500g)
Why Professional Bakers Use This System
Professional bakers trust baker's percentages because they deliver repeatability. A formula that works for one batch will work identically for the next batch, whether you're making 5 loaves or 50. The system removes emotion and guesswork.
For home bakers, baker's math transforms sourdough from mysterious alchemy into a transparent, scalable process. Write down your percentages once, adjust them based on your kitchen temperature and schedule, and you'll bake consistent loaves every time.
Start with a proven formula: 100% flour, 75% water, 20% starter, 2% salt. Once you master this, adjust percentages slightly to match your preferences and environment. That's how great sourdough bakers are born.