Dry Yeast Pitch Calculator: How Much Yeast?

This calculator works out how much dry yeast you need to pitch into your wort or must, based on batch volume, original gravity, and desired pitch rate. You enter your batch size in liters, the original gravity in Plato or specific gravity, and your target pitch rate in million cells per milliliter per degree Plato, and it returns the grams of dry yeast required. It also shows the total billions of cells needed so you can compare with the cell count stated on your yeast package.

Formula

The standard formula for yeast pitch rate is:

Cells needed (billion) = Volume (L) × Gravity (°P) × Pitch rate (million cells/mL/°P) / 1000

Then, to convert cells to grams of dry yeast:

Dry yeast (g) = Cells needed (billion) / 20 (billion cells per gram)

Where:

• Volume is the batch volume in liters (L).
• Gravity is the original gravity in degrees Plato (°P), which is roughly equal to specific gravity (SG) minus 1, multiplied by 4 (e.g., SG 1.050 ≈ 12.5 °P).
• Pitch rate is the desired cell density in million cells per milliliter per degree Plato (million/mL/°P).
• Cells needed is the total yeast cells in billions.
• Dry yeast needed is the weight in grams, assuming 20 billion viable cells per gram of dry yeast.

Worked Example

Using the default values: batch volume = 20 L, original gravity = 12 °P, pitch rate = 0.75 million/mL/°P.

1. Calculate cells needed: 20 L × 12 °P × 0.75 = 180 (million × L × °P) / 1000 = 180 billion cells.
2. Convert to dry yeast: 180 billion / 20 billion per gram = 9 grams.

So for a 20 L batch at 12 °P with a standard ale pitch rate, you need about 9 grams of dry yeast. This matches the calculator output.

Why Pitch Rate Matters

Pitching the right amount of yeast is one of the most important steps in brewing. Too little yeast leads to slow starts, increased risk of infection, and off-flavors from yeast stress (like diacetyl or esters). Too much yeast can strip nutrients and cause a overly clean, sometimes bland flavor, and may also produce excessive sulfur. The ideal pitch rate depends on the style and fermentation conditions:

• Ales: 0.75 million cells/mL/°P is a common target for standard ales.
• Lagers: 1.5 million cells/mL/°P is typical, because lager fermentations are colder and slower.
• High-gravity beers: For OG above 1.060, increase the rate by 10-20%.
• Pitching into high-ABV or sour worts: More yeast is needed to overcome harsh conditions.

Most dry yeast packages contain about 200 billion cells (i.e., 10 grams), enough for a 20 L batch of standard ale. However, viability decreases with age and storage temperature, so you may need to use more.

How to Use the Calculator

Enter your batch volume in liters (or convert from gallons: 1 gallon = 3.785 L). For original gravity, you can use a hydrometer or refractometer reading. If you only have specific gravity (SG), convert to °P using the approximate formula: °P ≈ (SG – 1) × 4. For example, SG 1.050 is about 12.5 °P. The pitch rate is a number you choose based on the style and your fermentation plan. The calculator then gives you the total cells and the grams of dry yeast.

Remember that dry yeast has about 20 billion viable cells per gram, but this can be lower if the yeast is old or stored poorly. Many brewers add a 10-20% buffer by rounding up to the nearest whole gram or using an extra half packet.

Common Mistakes and Misconceptions

One common mistake is confusing specific gravity with Plato. They are close but not identical: SG 1.050 is about 12.5 °P, not 50 °P. Using 50 °P in the calculator would give a wildly high number. Another mistake is forgetting to convert gallons to liters. Also, some brewers think all dry yeast has the same cell count per gram, but it varies by brand and batch; 20 billion is a reasonable average, but check the package if possible.

A frequent misconception is that you can “overpitch� dry yeast easily. In practice, overpitching is less of a problem with dry yeast than with liquid, because dry yeast is more resilient. However, pitching more than double the recommended amount can lead to a lack of yeast-derived flavor character.

Dry Yeast vs. Liquid Yeast

Dry yeast is cheaper, has a longer shelf life, and does not require a starter. Liquid yeast offers more strain variety but needs a starter to reach the same cell count. For example, a typical liquid yeast pack has about 100 billion cells, while a 10 g dry yeast packet has about 200 billion. So for a 20 L ale, you would need two liquid packs or one dry packet. For a lager, you might need four liquid packs or two dry packets. The calculator works for both, but the conversion to grams only applies to dry yeast.

Limits of the Formula

The formula assumes a constant cell count per gram of dry yeast (20 billion) and ignores viability loss. It also does not account for yeast health, wort nutrient content, or fermentation temperature. The pitch rate is a target, not a guarantee. For critical fermentations, some brewers use a microscope to count cells, but for most homebrewers, this calculator gives a solid estimate.

Also, the formula uses the original gravity in °P, which is a measure of extract (sugar) content. If you are using a refractometer reading in Brix, that is essentially the same as °P for wort, so you can use it directly.

Frequently Asked Questions

How many grams of dry yeast do I need for 5 gallons of ale?

5 gallons is about 19 liters. For a typical ale at OG 1.050 (12.5 °P) with a pitch rate of 0.75, the calculation is: 19 × 12.5 × 0.75 / 1000 = 178 billion cells, which is about 8.9 grams. So one 10 g packet is enough, with a little extra.

Can I use this calculator for liquid yeast?

Yes, the “cells needed� output works for liquid yeast too. But the grams output is only for dry yeast. For liquid yeast, you need to check the package cell count (often 100 billion) and make a starter to increase it if needed.

What is the ideal pitch rate for a lager?

Lagers typically need 1.5 million cells/mL/°P, which is double the ale rate. This is because lager fermentations are colder and slower, and the yeast needs more cells to finish cleanly. Using the calculator, a 20 L lager at 12 °P would need about 18 grams of dry yeast.

Does rehydrating dry yeast change the amount I need?

No, rehydration does not change the cell count. It just prepares the yeast for fermentation. The amount of dry yeast remains the same. However, rehydrating in warm water (about 30-35°C) can improve viability, so you might get closer to the 20 billion per gram assumption.

What if my original gravity is higher than 1.060?

For high-gravity worts, you should increase the pitch rate by 10-20% to avoid yeast stress. For example, if you normally use 0.75, use 0.9 for OG 1.070. The calculator lets you adjust the pitch rate to account for this.

How do I convert specific gravity to Plato?

A simple approximation is to take the last two digits of SG and divide by 4. For SG 1.050, that’s 50/4 = 12.5 °P. For SG 1.080, it’s 80/4 = 20 °P. This is accurate enough for pitch rate calculations.

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in v | Batch volume | L | 20 | 0
in g | Original gravity | °P | 12 | 1
in r | Pitch rate | million cells/ml/°P | 0.75 | 0.1
out cells | Yeast cells needed | billion | (v * g * r) / 1000 | 1
out grams | Dry yeast needed | g | cells / 20 | 1