How does the USAFA determine ACT/SAT conversions? What would a 28 Math ACT be equivalent to in the SAT? Thanks!

It's not really a conversion. It's a formula. GPA + Class Rank + Plus course difficulty/availability +..... + ACT = Academic score. But in-BETWEEN each of those "+" signs are formulas for calculating a composite score. If the SAT is used instead of the ACT, then the formula changes at that point. You can't do a direct conversion with your "28", because there aren't the same number of tests. ACT has 4 or 5 (depending if you take writing). SAT has 3. There is a conversion that some schools use; e.g 28 composite ACT is equal to 1880 CR+M+W; or a range of between 1860-1910. Unfortunately, it's difficult to say it's a direct correlation. But when used in the formula, it equals. I.e. a 36 on each ACT test and composite, once formulated, would equal an 800 on each SAT score. But you can't have a direct number comparison the way you're asking. It depends on each of the individual tests and the formula. Not just the composite.

You could convert the scores using percentiles, but as CC said, the Academy doesn't really see any need as they accept both test scores.