SRM Colour Calculator

How this works

The Standard Reference Method (SRM) is the standard beer-colour scale used in North American brewing, running from roughly 2 (pale straw) up past 40 (opaque near-black). It's measured in a lab by light absorbance through a beer sample, but homebrewers estimate it from a grain bill using a published approximation.

This calculator uses the Morey equation, the refinement of the older, simpler Daniels linear formula that most current brewing software has switched to because the linear version noticeably overstates colour on darker beers. The calculation runs in two steps: first, Malt Colour Units (MCU) are computed as the sum of each grain's weight (in pounds) times its colour (in degrees Lovibond), divided by batch volume in gallons. Then SRM itself is 1.4922 x MCU^0.6859 — the exponent below 1 is what corrects for the linear formula's tendency to overstate colour as MCU climbs.

The colour swatch is rendered from an aggregated approximation of widely published homebrew SRM colour charts. It's illustrative, not spectrophotometrically calibrated — no two screens will render the exact same colour for the same hex value either, so treat the swatch as a helpful visual reference for roughly where your beer sits on the pale-to-black spectrum, not a colorimetric proof.

What the formula doesn't account for

The Morey equation estimates colour contribution from the grain bill alone. Real finished beer can run measurably darker than the formula predicts for a few reasons the calculation has no way to see: a long, vigorous boil darkens wort through Maillard browning independent of the grain bill itself; high-melanoidin mash schedules (decoction, extended step mashing) produce additional colour compounds; and mash pH outside the normal range can shift extraction and colour development. Treat the result as a solid starting estimate for recipe planning, not a guarantee of the exact shade you'll pour.

Reading the result

If you're trying to hit a specific style's SRM range (check the style guideline pages for the target), remember that a small amount of very dark specialty grain moves SRM disproportionately more than a large amount of lightly-coloured base malt — a few hundred grams of a 300+ °Lovibond roasted malt can shift a pale beer's SRM by several points on its own, which is both a useful lever for fine-tuning colour and a common cause of a grain bill turning out darker than intended.

A worked example

4 kg of a 2 °Lovibond base malt plus 0.4 kg of a 40 °Lovibond crystal malt in a 19 L (5 gallon) batch computes to about 7.5 SRM — a light amber, comfortably within the American Pale Ale style range. Swap that crystal malt for the same weight of an 80 °Lovibond crystal — twice as dark on paper — and the result only rises to about 10.7 SRM, roughly a 40% increase rather than a doubling. That gap is the point of the exponent described above: because SRM scales as MCU raised to the 0.6859 power rather than in a straight line, a colour malt twice as dark does not produce a beer twice as dark. The shift is still real and visible — the beer moves noticeably toward a deeper amber — it's just smaller than a naive "double the Lovibond, double the colour" read of the numbers would predict.

Reading the swatch honestly

The rendered swatch is a single flat colour standing in for what is, in a real glass, a beer with depth, carbonation and clarity all affecting how the colour actually looks held up to light. Two beers with an identical calculated SRM can look noticeably different in person if one is hazy and one is bright-clear — the swatch is a useful planning reference for roughly where you're headed, not a substitute for looking at the beer itself once it's actually in a glass.