How Big a Starter Jar Do You Really Need? A Quick Start Guide to Baker's Math
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The short answer: keep as much starter as your recipe needs, plus a little extra for next time, in a jar that holds two to three times the volume of your just-fed starter. For most home bakers that means a Pint jar for 25–150g of starter and a Quart jar for 100–300g.
If that's all you came for, go bake. If you want to know why, and how to figure out the right amount of starter for any recipe you pick up, stick around. It takes about five minutes, and it's the most useful five minutes I've spent as a home baker.
Every recipe is secretly written in percentages
When a musician moves a song into a different key, every note shifts but the song stays the same, because the relationships between the notes stay the same. Baker's math works like that. It describes a loaf as a set of relationships, so you can make it bigger, smaller, or swap in your own starter without losing the song.
There's one rule: flour is always 100%. Everything else is written as a percentage of the flour weight.
Here's a plain, good-enough country loaf:
| Ingredient | Grams | Baker's % | How to read it |
|---|---|---|---|
| Flour | 500g | 100% | The anchor. Everything is measured against this. |
| Water | 375g | 75% | Also called "hydration." Higher = wetter dough. |
| Starter | 100g | 20% | How much of your sourdough starter goes in. |
| Salt | 10g | 2% | Remarkably consistent across almost every bread recipe. |
That's it. That's baker's math. You weigh the flour, and the percentages tell you everything else.
How much starter does a recipe need?
Most sourdough recipes use starter at 10–20% of the total flour weight. In grams, that usually lands somewhere between 50 and 120 grams of starter per loaf.
A couple of examples:
- One loaf with 600g of flour: 20% of 600 = 120g of starter.
- A three-loaf bake with 1500g of flour: 20% of 1500 = 300g of starter.
Reading a recipe backward
Picked up a recipe that just lists grams? Divide the starter by the flour.
A recipe calls for 150g of starter and 750g of flour. 150 ÷ 750 = 0.20 → 20% starter.
Now you know the recipe's "key," and you can transpose it to any size you like.
Scaling a recipe up or down
Want to double that 500g loaf? Double the flour to 1000g and let the percentages do the work: 750g water, 200g starter, 20g salt. No guessing.
How much starter should you keep?
Here's the part most guides skip. You don't just need enough starter for the recipe. You need enough to use in the recipe plus a little left behind to seed your next bake. A spoonful or two, around 20–30g, is plenty.
So work backward from your bake day:
Single loaf (needs 120g): Feed 30g starter + 60g flour + 60g water = 150g. Use 120g in your dough. The 30g left in the jar is your next starter. The loop closes itself.
Three-loaf bake (needs 300g): Feed 25g starter + 150g flour + 150g water = 325g. Use 300g. Keep 25g. Same loop, bigger batch.
Now, the jar
A healthy starter kept in the Goldilocks Zone (75–82°F / 24–28°C) typically doubles, and often triples, between feeding and peak. So your jar needs room for that rise, or you'll learn this lesson the way many of us did: by scraping starter off the lid, the shelf and occasionally the cat.
The rule: choose a jar at least two, and ideally three, times the volume of your just-fed starter.
For quick jar math, treat 1 gram of freshly fed starter as roughly 1 milliliter. It's not exact (starter is a bit denser than water before it gets bubbly), but it errs on the side of extra headroom, which is the direction you want to be wrong in.
- 150g of just-fed starter ≈ 150ml → rises to about 300–450ml → fits a Pint (500ml).
- 325g of just-fed starter ≈ 300–325ml → rises to about 650–975ml → fits a Quart (1000ml)
Quick reference
| What you're baking | Flour | Starter needed (10–20%) | Keep in jar | Jar |
|---|---|---|---|---|
| Just keeping it alive between bakes | n/a | n/a | 25–50g | Pint |
| One smaller loaf | 500g | 50–100g | 75–125g | Pint |
| One loaf | 600g | 60–120g | 90–150g | Pint |
| Two loaves | 1000g | 100–200g | 125–225g | Quart |
| Three loaves | 1500g | 150–300g | 175–325g | Quart |
| Bread for the whole block party | 3000g+ | 300–600g | a lot | Two Quarts, or a friend with one |
But...
- Not every recipe lives in the 10–20% range. Some long, cold fermentations use as little as 5%; some faster recipes go up to 30% or more. The math works the same; just plug in your recipe's number.
- Starters rise differently. Whole grain and rye starters can climb higher than white flour starters. Stiff (lower-hydration) starters rise less. If yours is an overachiever, size up.
- Temperature changes everything. A cold kitchen means a slower, lower rise. A warm, consistent spot means a more predictable peak, which is the whole reason we made Goldie.
- You don't need our jar to do any of this. Any clean jar with enough room will work. We designed ours with straight sides, no threads and no shoulder because it makes feeding, tracking and cleaning a lot less fussy. But flour, water, a jar and a scale will get you a great loaf.
Keep going
See Sourhouse Starter Jars
Pint (500ml) for 25–150g of starter. Quart (1000ml) for 100–300g.
Download the free sourhousv.commmunity Cookbook
More on caring for your starter, plus a bunch of sourdough recipes from our baker friends to put your new math to work.
