If you went through high school physics, you probably learned the cube rule: as you increase the size of an object, the surface area increases by the square of the linear size while the volume increases by the cube. Thus, if an object is twice as big in linear size, it has four times the surface area and eight times the volume.
The (often discredited) BMI or body-mass index formula is designed to provide a quick estimate of whether one is underweight, of normal weight, or overweight. The formula assumes that weight increases with the square of height rather than the cube, so it tends to overstate the BMI for tall folks.
This page provides a calculator which adjusts for this effect.