I'll try.
Mash Efficiency
Brew maths is really quite simple.
How it works is all malts and adjuncts etc give a different gravity.
The specifications are all written as H.W.E which is "hot water extract", with sugar being the highest at 386, so everything else is given as a % of that. ie, pale malt is around 81% which gives you around 309.
This is the total gravity you can get with 1 kilo in 1 litre but it is impossible to get this, this is 100% efficiency.
The same goes for American calculationss but its in P.P.G which is the gravity of 1 pound in 1 gallon. The same specs are used ie. 81% for pale malt gives you 37 points of gravity.
So a simple example to work out the total potential for 5 kg of pale malt in 23 litres is
5 x 309 / 23 = 67 (1.067)
Now to work out your efficiency you divide the gravity you achieved with this brew. Say you have 1.050 so 50/67 =.74 so you achieved 74% efficiency.
Then next time when you do the calc. 5 x 309 /23 =you simply times this by .74 .
This gives you your expected gravity.
For your first batches I would stick to using about 65 to 70%.
So do the 5 x 309/ 23 = 67.
then times 67 by .65 = 43(1.043)
PS: the HWE numbers are usually all on the malt craft sites. Other malts like crystal malt are around 75%. Some malts can be lower and some higher.
To get the number times 386 by the percent as a decimal point ie pale malt at 81% gives you 386 x .81 =312
Some examples:
Ale -------81% X 386 = 312
Pilsner----------------81%
Hoepfner Munich----80% 308
Melanoiden--------- -80%
Caramalt pils---------79% 305
Crystal---------------- 75%
Say the HWE is 308 litre degrees per kilogram for a malt.
That means 5kg in 20L will give you : (308 x 5)/20 = 77. i.e. 1.077 SG at 100% efficiency. Multiply that by your efficiency (eg. 75%) gives you 77 x 0.75 = 57.75 or close enough to 1.058.
Alternatively, use BeerSmith or a similar program, and it will work it out for you.
