Skip to main content
Redmoon Converters
🍺 Home Brewing

Grain Bill, Mash & Strike Water Calculator

Plan a recipe: per-grain percentages, predicted OG, SRM colour (Morey), mash thickness and strike water temperature (Palmer).

Built and maintained by Paul Clark, Redmoon Software · Checked against what this tool computes on

GrainWeightUnitPPG°L
Predicted OG · SRM
1.050 · 8 SRM
Total grain — · Strike water — qt @ — °F
Grain%Gravity ptsMCU
Quick reference

OG: SG = 1 + (Σ weight_lb × PPG × eff%) / batch_gal / 1000.

Color (Morey): SRM = 1.4922 × MCU^0.6859, where MCU = Σ(weight_lb × °L) / gallons.

Strike water (Palmer): T_strike = (0.2 / R) × (T_mash − T_grain) + T_mash, where R = qt/lb mash thickness (default 1.3).

Common grain PPG/°L: 2-row 37/2, Maris Otter 38/3, Munich 37/10, Vienna 35/4, Crystal 60L 34/60, Chocolate 28/350, Black Patent 25/525, Roasted Barley 25/300, Wheat 37/2, Pilsner 37/1.8.

How it works

Everything on this page comes from three published equations. Predicted gravity uses the points method: SG = 1 + (Σ weight_lb × PPG × efficiency) ÷ batch_gallons ÷ 1000, so 10 lb of 37 PPG malt at 72 percent efficiency into 5 gallons predicts roughly 1.053. Colour uses Morey's approximation, SRM = 1.4922 × MCU^0.6859, where MCU is Σ(weight_lb × °L) divided by gallons. Strike temperature uses Palmer's equation, T_strike = (0.2 ÷ R) × (T_mash − T_grain) + T_mash, with R the mash thickness in quarts per pound.

Efficiency and mash thickness move the headline numbers most. Efficiency defaults to 72 percent and scales every gravity point, so drop it toward 65 if you brew in a bag without a sparge. Mash thickness defaults to 1.3 qt/lb and drives both the strike volume, which is simply R multiplied by total grain weight, and the strike temperature. Selecting a named grain such as Crystal 60L or Roasted Barley auto-fills its PPG and °L; pick Custom to type your own values.

Two honest limits. The efficiency figure is applied to every grain equally, including crystal and roasted malts that give up most of their sugar without conversion, so dark recipes read a little low. And the strike figure is mash water only: it does not add sparge water, subtract the roughly 0.5 qt/lb the grain absorbs, or allow for boil-off, so it is not your total water requirement. Palmer's 0.2 constant also assumes a preheated tun; a cold cooler lands several degrees under target.

Frequently asked questions

Why did my actual OG come out below the predicted number?

Almost always efficiency. The prediction assumes exactly the efficiency percentage you entered, which defaults to 72. If you crushed coarse, mashed short or skipped a sparge, your real figure is lower. Brew once, measure, then enter your own number next time.

What mash thickness should I enter in qt/lb?

1.3 qt/lb is the default and a normal single-infusion figure. The field accepts 0.5 to 3.0. Thinner mashes hold temperature less steadily but need a smaller strike overshoot, because the 0.2 divided by R term in Palmer's equation shrinks as R grows.

How do I add a grain that isn't in the dropdown?

Choose Custom in that grain row, then type the PPG and °L yourself. The PPG field accepts 0 to 50 and the colour field 0 to 700, which spans everything from pilsner malt at 37 and 1.8 °L up to black patent at 25 and 525 °L.

Does the strike water figure include sparge water?

No. Strike water is mash thickness multiplied by total grain weight, expressed in quarts, and covers only what goes into the mash tun. Sparge volume, grain absorption and boil-off are not modelled here, so plan your full water volume separately.

How accurate is the SRM colour prediction?

Morey's equation is a curve fit that stays reasonable through roughly 30 SRM. Past that it under-reads badly, though the beer is opaque by then anyway. It also predicts wort colour rather than the darker finished beer that reaches the glass.

Efficiency is a property of your system

The 72% default is a typical homebrew mash efficiency, and it is the input that most affects the grain quantity. Efficiency depends on crush fineness, mash thickness, temperature control, sparge technique and equipment — it is a measured property of your setup, not a constant.

Which is why the first thing to do with this tool is brew once, measure the gravity you actually hit, and set efficiency to match. Until then the grain bill is a starting estimate.

Absorption, boil-off and hitting the volume

Grain absorbs roughly its own weight in water and keeps it, so a larger bill for a stronger beer reduces the wort you collect as well as increasing the sugar. Boil-off removes a further volume that depends on kettle geometry and boil vigour rather than on any standard figure.

Both have to be accounted for in the water calculation or you finish with the right gravity at the wrong volume, or the reverse. Measuring your own absorption and boil-off rate once is worth more than any published default.

Bigger beers also mash less efficiently, so a recipe scaled up in strength needs a lower efficiency figure than the same system achieves on an ordinary gravity.

Related tools