8.5 lb belgian pale

1.0 lb crystal 120l

1.0 lb belgian special B

0.5 ib american wheat

mash in 3.75 gallons

sparge 3.75 gallons

Total runnings 6.125 gallons

after boil 4.625 gallons (tons of boil off for 60 minutes eh??)

OG at 70F 1.065

From the

wiki malts chart (some of these are approximations):

Belgian Pale potential is 1.036 (actually that's Belgian Pils)

Crystal 120L potential is 1.034

Belgian Special B is 1.030

American Wheat malt is 1.038

So multiplying the potentials by the amounts and then dividing by the volume we have:

8.5 * 36 / 4.625 = 66.1

1 * 34 / 4.625 = 7.35

1 * 30 / 4.625 = 6.5

.5 * 38 /4.625 = 4.1

Add them all up to get 100% potential (i.e. max theoretical) @ 4.625 gal.:

66.1+7.35+6.5+4.1 = 84.05

Now divide your actual points by the max theoretical:

65/84.05=77.3% efficiency

That's your efficiency into the fermenter. People use different definitions for efficiency but using the info given the efficiency into the fermenter is about all we can calculate.