Yeast pitch rate calculator
Enter batch size, original gravity and the yeast you have (dry or liquid, how many packs, how old) to see how many cells you need and whether to make a starter or pitch more packs. For ales and lagers.
Runs in your browser. Nothing you enter is sent or stored.
How much yeast to pitch
Pitch rate is counted in million cells per milliliter of wort per degree Plato. Bigger batches and stronger worts need more yeast, so the cell count scales with both volume and gravity.
The calculator uses the rates from Yeast by Chris White and Jamil Zainasheff: 0.75 for ales, rising to 1.0 and 1.25 for high-gravity ales, and 1.5 for lagers. For 5 gallons (18.9 L) of a 1.050 (12.4 °P) ale that is about 176 billion cells. The same beer as a lager needs about 352 billion.
N = V × °P × R / 1000
- N
- Cells needed, in billions
- V
- Batch volume in mL
- °P
- Original gravity in °Plato (SG is converted first)
- R
- Pitch rate in million cells/mL/°P
| Beer | M cells/mL/°P |
|---|---|
| Ale up to 1.065 (15.9 °P) | 0.75 |
| Ale above 1.065 | 1.0 |
| Ale above 1.085 (20.4 °P) | 1.25 |
| Lager, any gravity | 1.5 |
Dry vs. liquid yeast
A fresh liquid pack from White Labs or Wyeast holds around 100 billion cells. In a 5 gallon batch that only covers very light beers below about 1.027. For a normal-strength ale it falls short, for a lager by far. You either pitch several packs or make a starter.
An 11 g packet of dry yeast holds roughly twice as many cells and keeps much better. The calculator assumes about 200 billion cells per packet, a common homebrew estimate. Manufacturers only guarantee a lower minimum, so treat it as a typical value. For most ales one fresh packet covers 5 gallons. For a lager, plan on two.
| Package | Billion cells |
|---|---|
| White Labs vial | 100 |
| Wyeast smack pack | 100 |
| Imperial pouch | 200 |
| Dry yeast, 11 g packet | 200 |
Viability: how yeast loses cells over time
Liquid yeast starts dying as soon as it is packaged. The calculator starts at 97% viability on the production date and loses about 21% per month, so a three-month-old pack has less than half its cells left. Always check the date on the pack before you decide whether you need a starter.
Dry yeast is far more stable. The calculator counts it at 100% until the best-before date, then applies a slow loss of 1.5% per month. You can change the monthly loss for both if your own experience or the supplier says otherwise.
v = 97 % × (1 − d)^(t / 30.44)
- v
- Viability on brew day
- d
- Monthly loss (21% for liquid yeast)
- t
- Days since the production date
Dry yeast: 100% up to the best-before date, then the same formula from 100% with 1.5% per month.
| Age | Viability |
|---|---|
| Fresh | 97% |
| 1 month | 77% |
| 2 months | 61% |
| 3 months | 48% |
| 4 months | 38% |
| 6 months | 24% |
Sizing a yeast starter
A starter is a small batch of wort that grows more yeast before brew day. When the viable cells in your liquid yeast fall short, the calculator plans a starter with the number of steps you choose and your largest flask, and shows how much dry malt extract (DME) to use.
On a stir plate it uses Kai Troester’s (Braukaiser) growth model: each gram of DME grows about 1.4 billion new cells as long as you start with no more than 1.4 billion cells per gram. With more yeast per gram the growth drops, and above 3.5 billion per gram the starter hardly grows at all. Without a stir plate it uses the growth curve from Yeast by White and Zainasheff, which grows fewer cells, up to about 200 million cells per mL. A fresh vial for a 5 gallon, 1.050 ale needs a stirred starter of about 0.6 liters with about 62 g (2.2 oz) of DME.
- Use about 100 g of DME per liter of starter, which gives a starter wort of roughly 1.036 (9 °P).
- A stir plate keeps the yeast in suspension and grows more cells from the same volume than an occasionally swirled flask.
- For a step starter, let each step ferment out, chill it, pour off the spent wort and add the next batch of fresh wort.
- Make the starter one to two days before brew day so it has time to finish.
- Dry yeast does not need a starter. If you need more cells, pitch another packet.
ΔN = 1.4 × DME (N / DME ≤ 1.4)
DME = V × 100
- N
- Cells you start the step with, in billions
- ΔN
- New cells the step grows, in billions
- V
- Starter volume in liters
- DME
- Dry malt extract in grams
On a stir plate. From 1.4 to 3.5 billion cells per gram, growth per gram is 2.33 − 0.67 × N / DME. The growth you need is split evenly over your steps, and no step is bigger than your flask. If your plan falls short, the calculator says how many steps or which flask would reach the target, and how many fresh packs to pitch with it otherwise.
Built into every BrewForge recipe
In BrewForge every yeast in your inventory is its own lot with lot number, manufacturing date and best-before date, so you know how old a pack is before you plan a starter. The same pitch rate and starter calculator is part of the app, and your recipe uses the yeast’s attenuation together with the mash schedule to predict final gravity.
- Yeast lots with manufacturing and best-before dates
- Supplier yeast catalogs with form, attenuation and temperature range
- Final gravity predicted from yeast and mash schedule
Use this calculator via API
The same calculation is also a free JSON API: no account, no key, one GET request. Handy for scripts, spreadsheets and AI assistants that should use exact brewing math instead of estimating it.
Add units=imperial (or one unit parameter per value) for °F, gallons and pounds. Every answer lists the inputs, the units and the formula it used.
GET https://brewforge.sh/api/public/calc/yeast-pitch-rate?og=1.050&volume=20&productionDate=2026-09-01&date=2026-10-15
FAQ
Questions & answers
How much dry yeast do I need for 5 gallons?
For an ale up to about 1.065, one fresh 11 g packet is usually enough: about 176 billion cells are needed for a 1.050 ale and a packet holds around 200 billion. For a lager of the same strength you need about twice that, so pitch two packets.
Do I need a starter for liquid yeast?
Usually, yes. A fresh liquid pack has around 100 billion cells, while a 5 gallon batch of a 1.050 ale needs about 176 billion. Only very light beers below about 1.027 get by with one fresh pack. Otherwise make a starter or pitch two packs, and more if the pack is a few months old.
Why do lagers need twice as much yeast?
Lager yeast works at low temperatures, where it grows more slowly. Pitching more cells up front makes up for that. The calculator uses 1.5 million cells per mL per °P for lagers, twice the ale rate of 0.75.
What happens if I underpitch?
The yeast has to grow more before it can ferment, so the lag phase gets longer and the yeast is stressed. That can mean more esters, fusel alcohols and diacetyl, or a fermentation that stalls before reaching final gravity. It matters most for lagers and strong beers.
Can I use yeast past its date?
Often, yes, with more cells. Liquid yeast loses about 21% of its viable cells per month, so an old pack needs a bigger starter. Dry yeast stays stable until the best-before date and loses cells slowly after that. Enter the date on the pack and the calculator adjusts the cell count.
What does million cells per mL per °Plato mean?
It is the standard way to express pitch rate. You multiply it by the wort volume in mL and the gravity in °Plato to get the number of cells. 0.75 million cells per mL per °P in 20 L of 12 °P wort is 20,000 × 12 × 0.75 = 180,000 million, or 180 billion cells.
Do the math once. BrewForge does it every brew.
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