I’ve organised to have my body donated to a medical school for dissection. It was quite complicated, lots of forms to be filled in and witnessed. My executor has to phone the university when I die & they send a van to collect me. They won’t accept my body if I’ve died of something communicable, or it was eg some accident that left me too mangled. When they’re done with me I’ll be cremated and my name goes up on a plaque in a special garden.
A BMI calculator will just use height and weight - if you have a lot of muscle bulk you’ll get a higher BMI result even if you’re lean. Conversely, some people are “thin on the outside, fat on the inside”, ie they carry a lot of visceral fat around their organs. So while BMI can be useful, it’s not perfect.