The 1/3/3 rule is a sourdough starter feeding ratio: 1 part starter, 3 parts flour, 3 parts water by weight. A 20 g spoonful of mature starter is fed 60 g flour and 60 g water, tripling the food supply on each feed. It is the slowest of the common feeds — used to stretch the time between feeds in cool UK kitchens, before holiday, or whenever you want a starter that peaks gently rather than racing.
What is the 1/3/3 rule?
What is the 1/3/3 rule for sourdough starter?
The 1/3/3 rule is a sourdough starter feeding ratio: 1 part mature starter, 3 parts flour, 3 parts water by weight. So 20 g of starter is fed 60 g flour and 60 g water. It is the slowest of the common feed ratios — used when you want to stretch the gap between feeds, in cool kitchens, or before a few days away from home.
The ratio in one line
The 1/3/3 rule is a ratio for feeding a sourdough starter, written in the order starter : flour : water. So 1 part starter, 3 parts flour, 3 parts water — all measured by weight, in grams. Some bakers write it as 1:3:3. Others as 1/3/3. They mean the same thing.
Why it's written as a ratio, not a recipe
The reason it's a ratio and not a recipe is that the absolute amount doesn't matter — only the proportions do. You can feed 10 g of starter with 30 g flour and 30 g water, or 50 g of starter with 150 g flour and 150 g water. Both are 1:3:3. Both behave the same way. Working in ratios is what lets you scale your starter up before a big bake and back down again after, without rewriting the method each time.
How to calculate a 1/3/3 feed (the maths)
How do you calculate sourdough feeding ratios?
To calculate a sourdough feeding ratio, weigh the starter you want to keep, then multiply by the two larger numbers in the ratio for flour and water. For a 1:3:3 feed: take starter weight, multiply by 3 for flour, multiply by 3 for water. 30 g starter becomes 30 g + 90 g flour + 90 g water — a total feed of 210 g.
Worked example — 20 g of starter
Say you have 20 g of starter left in the jar after your last feed (which is roughly a generous tablespoon). To feed it 1:3:3:
- Starter: 20 g (already in the jar)
- Flour: 20 × 3 = 60 g
- Water: 20 × 3 = 60 g
- Total weight after feed: 140 g
Stir until no dry flour is visible. Loosely cover. Leave at room temperature.
The lookup table — every common starter weight
| Starter you keep | Flour to add | Water to add | Total after feed |
|---|---|---|---|
| 10 g | 30 g | 30 g | 70 g |
| 20 g | 60 g | 60 g | 140 g |
| 30 g | 90 g | 90 g | 210 g |
| 50 g | 150 g | 150 g | 350 g |
| 75 g | 225 g | 225 g | 525 g |
| 100 g | 300 g | 300 g | 700 g |
A rule of thumb when you don't have scales to hand
If you have to eyeball it (don't, but if you must), one slightly heaped tablespoon of starter is about 20 g. Match it with four level tablespoons of flour (~60 g) and four tablespoons of water (~60 ml). It will be approximate. Buy digital scales — they cost £8 and they fix this.
1/3/3 Calculator
Slide to your starter weight, and we'll work out the feed and the expected peak time at three typical UK kitchen temperatures.
1/3/3 Feed Calculator
Starter20 g
Flour60 g
Water60 g
Total140 g
Expected peak time:
18°C12–20 h
22°C8–14 h
26°C6–10 h
Why it works — the slower-feed rationale
Food supply vs. microbial population
A starter is a living population of wild yeast and lactic-acid bacteria, eating the carbohydrates in the flour you feed them. On a 1:1:1 feed, the population eats through the food in 4–8 hours at room temperature and starts to go hungry. On a 1:3:3 feed, you've tripled the larder — the same population takes 8–14 hours to work through it. That extended runway is the whole point.
pH, peak height, and the slow climb
As the bacteria ferment, they produce lactic and acetic acid. The starter's pH drops from around 5.5 just after feeding down to 3.5–4.0 at full maturity (the curve is well documented in Buehler's Bread Science). On a 1:3:3 feed the climb is slower and the peak is gentler — the starter doubles or trebles in volume, holds for a few hours, then sinks. It's that "holding window" you want for baking and for less-frequent feeds.
When to use the 1/3/3 feed
When should I use a 1/3/3 feed?
Use a 1/3/3 feed when your kitchen sits at 16–18°C, when you're feeding once a day rather than twice, when you'll be away for one or two days, or when you want a milder, less tangy loaf. The bigger food supply slows the climb to peak and stops the starter going hungry between feeds.
Cool UK kitchens (16–18°C)
Most UK kitchens sit cooler than the 22°C the American baking blogs assume. February in a Yorkshire kitchen can be 15°C. Autumn in a Somerset kitchen, 17°C. A 1:1:1 fed starter at those temperatures will be sluggish by feed-time the next day — bigger food supply solves that.
Once-a-day or holiday schedules
If you'd rather feed once every 24 hours than twice, or you're heading away for a long weekend, 1:3:3 keeps the starter going without it souring. Three or four days at room temperature on a single 1:3:3 feed is realistic in a 16–18°C kitchen.
When you want a milder loaf
Bigger food supply = less acid produced per feed = a milder, less aggressively tangy loaf. If your bread has been coming out sharply sour, switching from 1:1:1 to 1:3:3 for the build-up feeds is one of the easiest ways to dial that down.
When NOT to use it
Active baking weeks
If you're baking two or three times a week and want a starter ready on demand, 1:1:1 is faster and more responsive. With a 1:3:3 you'll be waiting most of the morning for peak.
Warm kitchens above 22°C
In a warm kitchen (a south-facing flat in July, a proving drawer, a kitchen with the Aga on) the extra food doesn't slow things much — the warmth speeds them back up. You'll be back where you started.
Brand-new starters under 14 days old
A young starter still building its yeast and bacteria population struggles on a 1:3:3 — the population is too small to chew through the bigger food supply before it starts to spoil. Stick to 1:1:1 (or even 1:2:2) for the first two weeks. Once the starter is doubling reliably and smells sweet-yoghurty at peak, then consider 1:3:3.
1/3/3 vs 1:1:1 vs 1:5:5 — compared
Is 1/3/3 better than 1:1:1?
Neither is better — they suit different kitchens. 1:1:1 is the classic daily feed: starter peaks in 4–8 hours at 22°C and is ready when you are. 1:3:3 takes 8–14 hours to peak at the same temperature, giving you a longer window before the starter sours. Use 1:1:1 when baking weekly; switch to 1:3:3 in cool kitchens or before holiday.
Peak time at 22°C
How long does a 1/3/3 starter take to peak?
A 1/3/3 starter takes roughly 8–14 hours to peak at 22°C, 12–20 hours at 18°C, and as long as 24 hours at 15°C. The same starter on a 1:1:1 feed peaks in 4–8 hours at 22°C. Watch the starter, not the clock — peak is when it has doubled and the surface is domed but not yet sinking.
Peak time by feed ratio at 22°C ambient. Data from Bread Science (Buehler, 2006) plus our Somerset kitchen bake logs.
| Ratio | Peak at 22°C | Peak at 18°C | Typical use |
|---|---|---|---|
| 1:1:1 | 4–8 h | 6–12 h | Active baking, twice-daily feeds |
| 1:3:3 | 8–14 h | 12–20 h | Once-daily, cool kitchens, milder loaf |
| 1:5:5 | 14–20 h | 24+ h | Two days unattended, very mild flavour |
| 1:10:10 | 20–28 h | 36+ h | A weekend away |
Flavour profile
Smaller feeds (1:1:1) tend toward sharper, more lactic flavours. Bigger feeds (1:3:3, 1:5:5) tend toward milder, sweeter, more yoghurty notes — the starter has more food, produces less acid per gram.
How often you need to feed
Rough guide: feed once whenever the starter is past peak and starting to deflate. 1:1:1 means every 8–12 hours at room temp. 1:3:3 means every 18–24 hours. 1:5:5 means every 36–48 hours. None of this is rigid — read the starter, not the clock.
Frequently asked questions
What does 1/3/3 mean for sourdough?
1/3/3 is a sourdough starter feeding ratio: 1 part mature starter, 3 parts flour, 3 parts water, all by weight. So 20 g of starter is fed 60 g of flour and 60 g of water. It is the slowest of the three common feed ratios (1:1:1, 1:3:3, 1:5:5) and is used to stretch the time between feeds.
Is 1/3/3 the same as 1:3:3?
Yes — the two are interchangeable notations for the same feeding ratio. Some bakers write it with slashes (1/3/3), some with colons (1:3:3). Either way it means one part starter, three parts flour, three parts water by weight.
How long does a 1/3/3 starter take to peak?
At 22°C a 1/3/3 starter peaks in roughly 8–14 hours. At 18°C (a typical UK winter kitchen) it takes 12–20 hours. At 26°C (a warm summer kitchen) it can peak in 6–10 hours. Watch the starter rather than the clock — peak is when it has doubled or trebled and the surface is gently domed.
Can I use 1/3/3 with a new starter?
Not for the first two weeks. A young starter still building its yeast and bacteria population doesn't have the numbers to work through the bigger food supply before it spoils. Stick to 1:1:1 (or 1:2:2) until the starter is doubling reliably and smells sweet-yoghurty at peak — usually around day 14. Then you can move to 1/3/3 if it suits you.
Will 1/3/3 make my bread less sour?
Usually, yes. Bigger feeds mean less acid produced per gram of starter, so the loaf tends to come out milder and more yoghurty rather than sharply tangy. If your sourdough has been coming out too sour, switching your build-up feeds from 1:1:1 to 1:3:3 is one of the simplest ways to soften the flavour.
Can I use a 1/3/3 feed before going on holiday?
For a long weekend (2–4 days) in a cool 16–18°C UK kitchen, yes — a single 1/3/3 feed before you leave will usually be enough. For longer than that, move the starter to the fridge after feeding, or switch to a 1:5:5 / 1:10:10 feed. For more than a fortnight, dry the starter or freeze a portion.
What to read next
If your starter has gone quiet on you, if your starter has gone quiet walks through ten reasons and the fixes. For the full feeding schedule beyond just the ratio, see the feeding schedule we recommend. And our complete UK guide to sourdough starters is the pillar that ties it all together.
