Some people prefer lighter brews and some go for dark. For me, it depends on my mood. But if you want to know precisely what you’re getting yourself into before you pop open an ice cold can of alcoholic refreshment, it’s good to know that there exists a precise scientific scale for measuring the relative color of any beer.

Using a colorimeter, Joseph Williams Lovibond developed his scale in 1885 which is still used today. The Standard Reference Method—or SRMs—is measured out in degrees Lovibond, in honor of its inventor. Brewers can now use more advanced tools like spectrophotometers in order to establish the attenuation of light as it passes through a sample of their suds.

For a relative gauge of what particular style of beer might rank in terms of this scale, consider this: a super pale lager like Bud or Miller lite would be at around 2 SRMs. The slightly darker Pilsner Urquell pours at around 8 SRMs. Bass Pale Ale is closer to 20 SRMs while Guinness Stout eclipses 30 SRMs. Though as dark as Guinness appears to be, when held to a light source, a solid ruby red coloring emerges.

In actuality 30 is somewhere around the halfway point on this spectrum. Once you get down to truly black beers, like Imperial stouts, you’ll start to see SRMs approach 50, like Stone Brewing’s intense Russian Imperial Stout. With their robust, roasted grains, coffee stouts can get darker still. Goose Island’s Bourbon County Coffee, for example, clocks in at around 60 SRMs.

Although degrees Lovibond can be used to apply to whiskies or other sugar solutions, it is most commonly associated with beer and even still, is a scale of measurement that usually only ever concerns brewers. In fact, Sixpoint Brewery out of Brooklyn, NY, is one of the only microbrews that even bothers to display SRMs of the cans of their beer.

The next time you pour yourself a beer, get a little scientific and consider just how light or dark it might actually be. But expect to get some weird looks if you show up to the local watering hole with your own spectrophotometer.