Sourdough Baking Calculators: Levain Builder & Water Temperature Tool

Two of the most common questions in sourdough baking are "how much starter do I actually need?" and "what temperature should my water be?" Both come down to a bit of baker's math that's easy to get wrong by hand. Below are two sourdough baker's calculators that do that math for you — one builds any size levain, the other dials in your mixing water temperature so your dough hits its target every time.

How the Levain Builder does the math

Every levain build comes down to three numbers: how much you need (target weight), how wet it should be (hydration), and how much starter to seed it with (inoculation). The calculator assumes your ripe starter is itself kept at roughly 100% hydration — equal parts flour and water — which is standard for most home bakers. From there, it works out how much total flour the finished levain needs, splits that between what you add fresh and what's already inside your starter based on your seed percentage, and fills in water to hit your target weight. Check it against a classic 1:2:2 feeding (1 part starter, 2 parts flour, 2 parts water): that's 50% inoculation at 100% hydration, and for a 100g levain it comes out to 40g flour, 20g starter, and 40g water.

The ripeness gauge follows the same logic bakers have relied on for years: a smaller seed means fewer microbes doing the work, so it takes longer but builds more sourness; a bigger seed ripens fast with a milder flavor. It's a planning guide, not a stopwatch — confirm your levain is ready by sight, smell, and the float test (a spoonful should float when dropped into water).

How the Water Temperature Calculator works

Water is the easiest lever for controlling your final dough temperature, because it's the one ingredient you can quickly heat or cool right before mixing. The calculator uses the four-factor Desired Dough Temperature (DDT) method — the standard approach used for doughs built with a levain or other preferment: multiply your desired dough temperature by four, then subtract your flour temperature, room temperature, levain temperature, and a friction factor (the heat your mixing method adds).

Friction factor depends on how you mix: hand mixing or light folding adds very little heat (0–2°C), a stand mixer typically adds more (roughly 6–12°C depending on speed and time), and longer or more vigorous machine mixing adds more still. If you're not sure, start with a low estimate and refine it next time by comparing your calculator's prediction to the dough temperature you actually measure after mixing.

Using both calculators together

Plan backward from when you want to bake: pick your levain build (seed % and hydration) based on how much time you have, use the ripeness gauge to know roughly when it'll peak, and use the water temperature calculator right before mixing so your final dough lands at the same target temperature your levain was built at. Keeping these numbers consistent bake to bake is one of the simplest ways to get more predictable results. For more on keeping a starter healthy between bakes, see our Starter Care Guide.