Most scaling disasters aren't a math problem. The baker multiplied everything correctly โ flour, water, salt, starter, all by exactly 1.5 โ and the loaf still came out underbaked, oddly shaped, or weirdly fermented. If that sounds familiar, the issue isn't arithmetic. It's that not everything in bread scales the same way.
Some things scale linearly. Some don't scale at all. And a few things โ including bake time and bulk fermentation โ scale in ways that surprise people the first time around.
Here's what actually changes when you size a recipe up or down, and how to handle each part.
Most sourdough recipes online are written for a single loaf with around 500g of flour. That makes a roughly 800โ900g loaf, depending on hydration. Sometimes you want more than one loaf. Sometimes you have a smaller Dutch oven, or you bought a banneton that holds 750g. Sometimes you're feeding a crowd, or testing a recipe and don't want to waste flour.
You also might be working backwards: you want a 1kg finished loaf for a holiday meal, and you need to figure out how much flour, water, salt, and starter to use to land there.
The flexibility to scale is one of the things baker's percentage was designed for. If you're new to that idea, the baker's percentage explainer walks through how it works.
These ingredients can be multiplied straight across with no fuss:
If your recipe is 500g flour, 375g water (75% hydration), 10g salt (2%), and 100g starter (20%), then a 1.5x scale is simply 750g flour, 562g water, 15g salt, and 150g starter. The dough behaves the same. The percentages haven't changed.
This is why bakers think in percentages rather than fixed amounts. The recipe stays valid at any size.
This is where most home bakers run into trouble. A handful of things either change non-linearly or don't change at all when you size up or down.
A bigger mass of dough holds heat differently than a smaller one. A 1kg dough in a bowl ferments slightly faster than 500g of dough in the same room, because the larger mass insulates itself and stays warmer at the core. The difference isn't huge โ usually 10 to 20 minutes on a typical bulk โ but it's real, and it gets bigger as the batch gets bigger.
If you're scaling from a single loaf to four loaves at once, expect bulk to finish 20โ40 minutes earlier than the original recipe says. Don't trust the clock. Watch the dough.
A bigger loaf has proportionally less surface area for its mass. That changes everything from how fast it dries out during proof to how thick the crust gets to how long it takes the heat to reach the center during the bake. A 1.5kg loaf is not just a bigger version of a 750g loaf โ it's structurally different.
The practical impact: scoring is more important on a big loaf (because there's more dough that needs to expand), and steam during the first part of the bake matters more.
This is the one most people get wrong. Bake time scales roughly with weight, but not in a 1:1 way. A loaf twice as heavy takes longer than twice as long if you don't compensate.
A rough working rule:
| Loaf weight | Bake time at 230ยฐC / 450ยฐF (covered + uncovered) |
|---|---|
| 500g | 20 min covered + 20 min uncovered |
| 750g | 22 min covered + 23 min uncovered |
| 1kg | 25 min covered + 25 min uncovered |
| 1.5kg | 28 min covered + 30 min uncovered |
| 2kg | 30+ min covered + 35+ min uncovered (and consider lowering temp by 10ยฐC in the second half) |
Above about 1.5kg, you generally want to drop the oven temperature for the second half of the bake. The crust will burn before the inside is done if you don't.
The most reliable way to know when a loaf is baked is internal temperature: 96โ99ยฐC (205โ210ยฐF) at the center for a fully baked sourdough. A cheap probe thermometer ends the guessing.
Salt at exactly 2% is a starting point, not a law. Some bakers prefer 1.8%, some go up to 2.2% โ especially with whole grain flours, which can taste flat at lower salt levels. When you scale up, this still holds. But if you're scaling a recipe you've been making for years and you've already adjusted the salt to suit your taste, keep that adjusted percentage. Don't revert to 2% just because you're scaling.
Folding a 500g dough takes about 10 seconds. Folding a 2kg dough takes longer, requires more stretching, and your hands tire faster. The technique doesn't scale โ your effort does. Plan for it. Big batches benefit from longer initial mixes (autolyse, slap-and-fold) and fewer, more deliberate folds rather than many small ones.
You can't scale a Dutch oven. If your recipe is designed for a 4-quart Dutch oven and you double the dough, you have to either bake two loaves in sequence or split the dough between two vessels. A single huge loaf in a too-small Dutch oven will hit the lid as it expands and end up dense and oddly shaped.
The same applies to bannetons, oven space, fridge space for cold retard, and dough containers for bulk fermentation. Scale equipment along with quantity, not after.
Say you've been making a recipe with 500g flour and you want to bump it up to 800g flour for a slightly larger loaf.
Original recipe:
Multiplier: 800 รท 500 = 1.6
Scaled recipe:
Final dough weight: 1576g (versus the original 985g). That's about a 60% bigger loaf.
What changes in practice:
This is exactly the kind of math the sourdough calculator handles in one step. Enter the original recipe, set the multiplier to 1.6, and it scales every ingredient in proportion. You only need to think about what doesn't scale โ the timing and equipment.
Scaling down has its own quirks. The math is identical โ just multiply by something less than 1 โ but the practical issues differ:
Sometimes you're not just scaling size โ you're also adjusting hydration to match a different flour, a different oven, or a different season. (Yes, kitchens get more humid in summer; some bakers drop hydration by 2โ3% in muggy weather.)
You can change hydration independently of scaling. The two adjustments are unrelated. The calculator handles both together: enter the new size, enter the target hydration, and it figures out the water amount that hits both targets.
If you're new to choosing a hydration, the hydration guide has a full breakdown of what each percentage feels like in the hand.
A few patterns that repeatedly trip people up:
Forgetting that starter contains flour and water. When you scale starter, you're scaling both the flour and water inside it. If your recipe assumes 100% hydration starter and you use a 50% (stiff) starter at the same weight, the dough's actual hydration drops noticeably. The starter hydration guide covers how to handle this.
Rounding too aggressively. "10g salt becomes 16g salt" is fine. But rounding 16.4g to 16g across many ingredients adds up, especially in a small batch. Keep one decimal where it matters.
Not adjusting bake time. This is the single most common reason scaled-up loaves come out gummy in the middle. If you doubled the dough, you cannot bake for the original time and expect the same result.
Trying to scale on the day of the bake. Scaling changes timing. If you're already mid-bulk and decide to dump in more flour to make a bigger loaf, you're going to throw off the fermentation. Plan the scale before you mix.
Think of a sourdough recipe as two separate things bolted together: a formula (the percentages) and a process (the timings, equipment, and technique). Baker's percentage scales the formula automatically. The process needs human judgment.
When you internalize that, scaling stops being scary. The numbers take care of themselves. Your job is to watch the dough, watch the oven, and adjust the parts of the process that don't fit the new size.
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