Can someone please help me out with how to properly calculate conversion efficiency using the Brewers friend calculator (found here and set to conversion efficiency: https://www.brewersfriend.com/brewhouse-efficiency/).

My last brew was 5kg Maris Otter, 500g Wheat and 250g Oats. Gravity was 1.055. Now I am not sure what Volume to put in the calculator. I had 15L mash water and added roughly 16L sparge, bringing the total to 31L added, although due to grain absorption I had 26.5L in the kettle (robobrew) post-sparge. I ended up with 23.5L post boil.

Thanks in advance.

  • Have a look at braukaiser's page on understanding efficiency. If you're looking for the conversion efficiency, the sparge volume doesn't factor into it. If you want your conversion and lauter efficiency, then that is different again. In short, conversion efficiency is how much starch you can convert, lauter efficiency is how much you can rinse out, and mash efficiency is an aggregate of both. I would personally recommend looking into the calculations yourself, rather than using brewer's friend, if you're interested in this stuff.
    – Frazbro
    Commented Mar 17, 2019 at 9:25
  • Link here: braukaiser.com/wiki/index.php/Understanding_Efficiency
    – Frazbro
    Commented Mar 18, 2019 at 1:12

1 Answer 1


I've punched your numbers in, and it looks like 26.5L is probably close to the right number. It's not a very clear calculator though, so I would recommend heading to http://braukaiser.com/wiki/index.php/Understanding_Efficiency and reading up on the matter, then deciding what sort of efficiency you want to understand. Brewer's friend combines conversion and extraction/lauter efficiency into one misnamed term (I would call it Mash efficiency, as it incorporates both key elements of mashing).

To measure conversion efficiency, all you need is the grist ratio and the weighted average yield of the grain, and the measurement you take after conversion is complete, and before you add any sparge liquid. This tells you how much starch was converted to sugars.

To measure lauter efficiency, you work out how much sugar is in the mash using the conversion efficiency, then figure out how much you managed to get out of the mash and into the kettle.

Total mash efficiency combines these two concepts, but the BF calculator doesn't really go into this, but is does say, kind of in passing, that your volume should exclude grain absorption and mash tun dead space, and your gravity should be a blend of all runnings. So it sounds like 26.5L for you.

  • Alright thanks, I'm getting somewhere: Brewers Friend - 5.75kg, 26.5L (preboil), plus 1.050 gravity = 75% Grainfather calc - 5.75kg, 26.5L (preboil), plus 1.050 gravity = 75% link - grainfather.com/brewing-calculators?___store=uk I can't get the maths to work using Braukaiser though -
    – W4K1NG
    Commented Mar 21, 2019 at 1:46
  • Braukaiser - 26.5L and 5.75, converts 4.5 mash thickness, say 14.6P. Then OG reading of 12.5 = 85%. I'm looking at overall efficiency then, have a robobrew, so it's all in one kettle. Cheers
    – W4K1NG
    Commented Mar 21, 2019 at 1:54
  • It looks like the Grainfather calc doesn't account for your grist at all, what did you decide your aggregate yield was for the grain bill? I'm glad you're getting to where you want to go
    – Frazbro
    Commented Mar 21, 2019 at 2:20

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