# Bethe–Feynman formula

The Bethe-Feynman efficiency formula, a simple method for calculating the yield of a fission bomb,[1] was first derived in 1943 after development in 1942. Aspects of the formula are speculated to be secret restricted data.[2]

## Related formula

• a = internal energy per gram
• b = growth rate
$a \approx (bc)^2 f$