How is the scaling factor calculated?

The scaling factor is simply the new batch volume divided by the original batch volume. Every grain, hop, and adjunct weight is multiplied by this single factor, so all ratios stay identical and the original gravity is preserved.

Does doubling the batch double the bitterness?

Not exactly. Doubling the recipe doubles the hop mass, which keeps the hop-to-wort ratio constant, but hop utilisation also depends on wort gravity and boil volume. If your boil volume scales proportionally, IBU stays close; if it does not, recalculate IBU with a Tinseth or Rager formula.

Can I scale down a 5-gallon recipe to a 1-gallon test batch?

Yes. Enter 5 as the original and 1 as the new volume; the factor becomes 0.2 and every ingredient is multiplied by 0.2. Small test batches are a cheap way to trial a recipe before committing a full brew day.

Should I scale the yeast the same way?

Yeast pitch rate scales with both volume and gravity, not linearly with the grain bill, so use a dedicated pitch-rate calculator. As a rough guide, a larger batch needs proportionally more yeast cells to ferment cleanly.

Does mash water scale with the grains?

Strike and sparge water scale with the grain bill if you keep the same mash thickness (litres per kg). The calculator scales ingredients only; multiply your water volumes by the same factor to keep your mash ratio consistent.

Brew Batch Scaling Calculator

The Brew Batch Scaling Calculator resizes a homebrew recipe to a new batch volume while keeping every ingredient ratio identical. Whether you are bumping a 5-gallon recipe to 10 gallons or shrinking it to a 1-gallon pilot, it multiplies each grain, hop, and adjunct by a single scaling factor so the original gravity and balance are preserved.

How it works

Scaling a recipe is pure proportion. The calculator computes one number — the scaling factor — and applies it to everything:

scaling factor = new batch volume ÷ original batch volume

If a recipe was written for 19 L and you want 38 L, the factor is 38 ÷ 19 = 2.0, so every weight doubles. For a 1-gallon test batch from a 5-gallon recipe the factor is 0.2, and each amount drops to one-fifth.

Because all ingredients are multiplied by the same factor, the grist ratios, the hop-to-wort ratio, and therefore the target original gravity stay the same. The only quantity that does not scale perfectly linearly is hop bitterness.

Hop utilisation note

Bitterness (IBU) depends on how much of the alpha acid is isomerised during the boil, and that utilisation changes with boil gravity and boil volume. When you scale the recipe and your boil volume scales by the same factor, IBU stays close to the original. But if your kettle forces a different boil-volume ratio — for example a concentrated boil on a small system — the utilisation shifts and you should recompute IBU. The tool flags this whenever the scaling factor moves far from 1.0.

Example

A 23 L pale ale uses 4.5 kg pale malt, 0.5 kg crystal, 30 g of bittering hops and 20 g of aroma hops. Scaling to 46 L (factor 2.0) gives 9.0 kg pale malt, 1.0 kg crystal, 60 g bittering hops and 40 g aroma hops. Keep the same mash thickness and double your strike and sparge water to match.