Windsurf Sail Size Calculator (Weight & Wind Speed)
Find the right windsurf sail size in square meters from your weight and the wind speed in knots, km/h, mph or m/s, with a sail quiver chart for 10–35 knots.
How it works
Sail area (m²) ≈ 1.34 × rider weight (kg) ÷ wind speed (knots) · 1 knot = 1.852 km/h = 1.151 mph = 0.514 m/s.
Windsurfing sail charts follow a simple pattern: the sail you need grows with your weight and shrinks as the wind gets stronger. The rule of thumb 1.34 × weight ÷ knots reproduces the standard planing charts closely (a 70 kg rider needs about 9.4 m² in 10 knots and 4.7–4.8 m² in 20 knots). It assumes you want to plane on a board suited to the conditions; beginners learning in light wind use much smaller sails (3–5.5 m²) regardless of the formula, and wave sailors rig a little smaller.
Worked example
A 75 kg rider in 15 knots of wind: sail size = 1.34 × 75 ÷ 15 = 6.7 m². In 20 knots the same rider would drop to 5.0 m², and in 12 knots go up to 8.4 m².
Sources: SurferToday — Windsurf board and sail size charts · Beaufort wind scale and unit conversions — NOAA
Frequently asked questions
What size windsurf sail do I need?
Multiply your weight in kg by 1.34 and divide by the wind speed in knots. A 75 kg sailor in 15 knots needs about 6.7 m²; in 25 knots about 4.0 m².
What sail size should a beginner use?
Beginners learning to uphaul and steer should use small, light sails — about 3–4 m² for teenagers and light adults, 4.5–5.5 m² for heavier adults — in light, steady wind. The formula is for planing once you can sail in the harness.
How many sails do I need in a quiver?
Most recreational sailors cover 12–30 knots with three or four sails spaced about 1–1.5 m² apart, for example 7.5, 6.2, 5.3 and 4.5 m² for a 75–80 kg rider.
Does board size matter too?
Yes. Big sails need a wider, higher-volume board to plane early, and small sails pair with smaller boards. As a starting point, beginners ride boards with volume of at least their weight in kg plus 80–100 liters.
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This calculator is for educational purposes. Double-check important results before acting on them.