Block Coefficient Calculator

About this calculator

A ship's block coefficient (Cb) is the ratio of its underwater hull volume to the volume of a rectangular box with the same length (at waterline), beam, and draft: Cb = ∇ / (L × B × T). It's a dimensionless number between roughly 0.5 and 0.9 — a slender, fine-lined hull like a naval frigate has a low Cb (~0.5), while a bulk carrier or tanker built to maximize cargo volume has a high Cb (~0.85), since it fills far more of that bounding box.

Naval architects use block coefficient in the earliest stages of hull design to balance cargo capacity against resistance and speed, since a fuller hull (higher Cb) carries more cargo per unit length but pushes more water and burns more fuel at a given speed than a finer one.