Sail Area to Displacement (SA/D) Calculator
Enter your sail area and displacement to get the SA/D ratio, a quick power-to-weight measure that hints at how lively a sailboat will feel.
How to calculate the SA/D ratio
- Enter the total sail area in square feet (mainsail plus 100 percent foretriangle).
- Enter the boat's displacement (weight) in pounds.
- Read the SA/D ratio and its performance band.
Examples
500 sq ft sail, 10,000 lb boat
sailAreaSqFt = 500, displacementLb = 10000
Displacement 156.25 cu ft, SA/D 17.24 (moderate cruiser/racer)
Frequently asked questions
What is the SA/D ratio?
Sail area to displacement is a power-to-weight figure for sailboats. It divides sail area by the displacement volume raised to the two-thirds power, so it compares boats of different sizes fairly.
What do the numbers mean?
As a guide, under 16 is a heavy cruiser, 16 to 20 is a moderate cruiser/racer, 20 to 24 is a performance boat and 24 or more is a racer. These bands are rough, not strict.
Why divide weight by 64?
Displacement is a weight, but the ratio needs a volume. Dividing pounds by 64, the weight of a cubic foot of seawater, converts the weight into cubic feet.
Which sail area should I use?
Use the mainsail area plus the 100 percent foretriangle, the standard measure designers quote. Do not add overlapping genoa or spinnaker area.
Is a higher SA/D always better?
Not always. A high ratio means more sail power and speed in light air, but it also means more heeling and a need to reef sooner as the wind builds.
Related tools
Hull Speed Calculator
Calculate the theoretical hull speed of a displacement boat from its waterline length. Get the result in knots, mph and km/h with the formula shown.
Beaufort Scale Calculator
Convert wind speed in knots to a Beaufort force number. See the force, its sea-state description and the typical wave height for that wind.
Anchor Scope Calculator
Calculate how much anchor rode to let out from water depth, bow height, scope ratio and tide. Get the total height and rode length in feet with the formula.
Boat Fuel Calculator
Estimate trip fuel for a powerboat from distance, speed, gallons per hour and a safety reserve. See hours underway and base and total fuel in gallons.
Distance to Horizon Calculator
Calculate how far away the horizon is from your eye height. Get the distance in nautical miles, statute miles and kilometres with the formula shown.