Sail Area / Displacement Ratio Calculator
Enter sail area and displacement to compute the SA/D ratio — a sailboat's power-to-weight measure.
Square feetSquare metres (100% foretriangle + mainsail).
Pounds.Kilograms.
The SA/D formula
SA/D = Sail area(ft²) ÷ (Displacement(lb) ÷ 64)^(2/3). Dividing displacement by 64 (the weight of a cubic foot of seawater) converts weight to displaced volume; the two-thirds power turns volume into an area, so the ratio is dimensionless.
How to read it
- Under 16 — under-canvassed; needs breeze or motorsailing.
- 16–20 — typical cruiser, good all-round performance.
- Over 20 — powered-up racer / performance cruiser.