Sail Area to Displacement Ratio (SA/D)

This is the "horsepower-to-weight" ratio for a sailboat. It indicates how much power the sail plan has relative to the boat's mass.

Formula:

SA/D = SA / ( (D / 64) ^ (2/3) )

SA = Sail Area in square feet (usually the area of the mainsail + 100% of the foretriangle)
D = Displacement in pounds
64 = The approximate weight of one cubic foot of seawater in pounds

Under 14-15: Underpowered. Typical of heavy, motorsailer-type offshore cruisers. Will require motoring in light winds but can be very forgiving.
16 - 19: Moderate. The sweet spot for most coastal and offshore cruising boats. Enough power to sail well in a variety of conditions without being overwhelming.
20 - 24: Performance-oriented. Common for cruiser/racers. The boat will feel lively, accelerate quickly, and perform well in light air, but may need to be reefed sooner.
Above 25: High performance/Racing. Expect thrilling acceleration. These boats can be twitchy and physically demanding, requiring an experienced crew.

For the Owner: Are you looking for a gentle floating cottage (low SA/D) or a spirited sports car (high SA/D)? Your answer will guide your target range.

Below are some example boats with their sail area and displacement values. You can use the calculator to find the SA/D ratio for your own boat.

Catalina 30

Beneteau Oceanis 38

J/109

Melges 24