Comment by Merad

You're looking for Young's penetration equations, developed at Sandia National Lab in the 90s. Your favorite LLM can walk through the math step by step if you're interested, but a US WW2 era AN-M64 500 lb bomb gives results of 15-20 ft penetration in average soil. Reality might be a little less because free-falling bombs have forward velocity from the aircraft that dropped them, so they hit at angle instead of penetrating straight down.