Work out surface area to volume (cell) instantly with clear inputs, formula shown and shareable results.
Calculates surface area and volume for the chosen cell geometry and divides them, the ratio that limits how large a cell can grow.
Surface area to volume
Sphere: A = 4(pi)r^2, V = (4/3)(pi)r^3, so A/V = 3/r. Cube: A = 6s^2, V = s^3, so A/V = 6/s
Exchange happens across the surface while demand scales with volume, so large cells cannot supply their interior by diffusion.
Flattened or elongated shapes, microvilli, internal membranes and cytoplasmic streaming all raise effective exchange.