Yeast Pitch Rate Calculator

What this calculator does

Pitch the right number of healthy cells — every batch.

Pitch rate = target cell density × volume × gravity in °Plato. Underpitch and the yeast is stressed: sluggish or stuck fermentation, excess esters and fusels, diacetyl that won't clean up. Overpitch and you strip the character you were aiming for, with thin, muted beer. This tool does the fiddly cell math for you and converts it into the three things you actually buy — liquid packs, grams of dry yeast, or a starter target — so you hit the pitch you intended, not the one you guessed.

Everything runs client-side. Nothing is stored, nothing is sent — change any input and the result updates live.

The pitch rate formula, explained

The math behind the number.

Cells = rate (M/mL/°P) × volume (mL) × gravity (°P)

The industry-standard pitch equation multiplies three things: your target cell density (in million cells per millilitre per degree Plato), your volume in millilitres, and your wort's gravity in degrees Plato. The result is a raw cell count in millions, which this tool rolls up into billions and packages.

Ale vs lager: why lager needs ~2× the cells

The classic targets are 0.75 million cells/mL/°P for ales and 1.5 for lagers — roughly double. Lagers ferment cold, where yeast is metabolically slower and reproduces less, so you compensate with a bigger starting population to get a clean, sulfur-free, well-attenuated fermentation. Big beers of either type push the rate up again: high-gravity worts (OG > 1.065) stress yeast harder, so 1.0 for a strong ale and up toward 2.0 for a big lager are common. Pick the closest preset, or enter your own under Custom.

Converting SG to °Plato (and why the app does it for you)

The formula needs gravity in degrees Plato, but most homebrewers read specific gravity off a hydrometer. The tool converts automatically using the standard cubic polynomial, so you can type 1.055 and it works in 13.6 °P under the hood:

Pitching by slurry or starter volume

Most working breweries don't pitch by the pack — they pitch a measured volume of yeast slurry harvested from a previous batch, or the volume of a starter they grew. Both are just cells suspended in liquid, so the same total-cell target applies: divide the cells you need by the slurry or starter's cell density to get millilitres. Switch the Pitch from tabs on the result to Slurry or Starter and set the density that matches your yeast.

The catch is that density is a real variable, not a constant. A thick, decanted repitch slurry runs around 1 billion cells/mL, but a trub-heavy or looser one is lower and a very clean, tightly-packed one higher — so slurry cell density is the single number most worth confirming with a cell count before you trust it. A finished stir-plate starter lands near 0.15–0.2 billion cells/mL; a still (unstirred) starter closer to 0.1. If you're pitching off slurry or a starter, you should already have a count — enter that measured cells/mL (in millions or billions per mL) and the tool gives you the exact volume; the conservative defaults are only a fallback for when you haven't counted.

The part no calculator farm writes

When the standard pitch rate is wrong.

The presets are a starting point, not gospel. Here's where the "just use 0.75" advice quietly costs you a batch.

High-gravity worts (> 1.065): scale up or stress the yeast

Above ~1.065 the wort is a harsher environment — higher osmotic pressure, more alcohol to survive, more to attenuate. Pitching an ale-standard 0.75 into a 1.085 imperial stout under-provisions the crop and you'll taste it as hot solvents and a stall. Move to 1.0–1.25 for big ales, and pair the higher pitch with good aeration/oxygenation — cells need O₂ to build healthy membranes before they multiply.

The overpitching myth for big beers

Brewers hear "overpitching strips character" and under-pitch their biggest beers to protect flavor. For high-gravity worts that's backwards: the wort is so rich that a "high" pitch is really just adequate. The character risk from overpitching is real in small, delicate beers — not in a barleywine.

Repitching from a healthy crop vs a fresh pack

Harvested yeast from a previous batch can be pitched by slurry volume and density rather than pack count — but only if you know the concentration. A thick, healthy first-generation slurry is dense; an old, trub-heavy one is mostly dead cells and cold break. Count it (hemocytometer) before you trust it, or you're guessing at the one number that matters most.

Viability decay: an old pack isn't the count on the label

A liquid pack loses roughly 20–25% of its viable cells per month. A "100 billion" pack three months old is closer to 40–50 billion — pitch it as fresh and you've silently under-pitched by half. Drop the viability % in the calculator to match the pack's age and the required packs/grams scale up accordingly. Don't know the number? Estimate it with the viability calculator →

Notes from the lab