Fin & Foil Calculator

The right fin length depends on your weight, sail size, board width and discipline. Rule of thumb for slalom: 30-34 cm with a 7.5 m² sail. For freeride 28-32 cm, for wave 18-24 cm and for freestyle 16-22 cm. The calculator works it out exactly based on your input — including weed fin correction and separate sizes for G10 versus carbon fins.

Wing size depends on your weight and the wind. For a 75-85 kg rider in 15-20 knot wind, a 5.0 m² wing is standard. For lighter wind (10-15 knots) you'll want 6.0-7.0 m²; for strong wind (25+ knots), 3.5-4.0 m². Most wing foilers have two sizes in their quiver to cover the full wind range. The calculator uses this input to determine your foil size.

Heavier riders, light wind or beginners need a larger front wing — typically 1500-2200 cm² with a low aspect profile. Intermediate riders usually use 1200-1500 cm². Advanced riders in strong wind can use 800-1200 cm² high aspect. The calculator provides three sizes — low, mid and high aspect — matched to your weight and wing size.

For a beginner kite foiler, a large front wing is essential: 900-1200 cm², thick profiles, low aspect ratio. This provides early lift, stable handling and forgiving behavior on touch-downs. Move to 500-800 cm² high aspect race foils only at advanced level. Combine with a shorter mast (55-65 cm) for extra control as a beginner.

This classic rule of thumb works reasonably for traditional long-narrow boards but is outdated for the current generation of short, wide boards. A 7.5 m² sail would suggest a 41.5 cm fin — in practice that's way too long for modern slalom boards 75-85 cm wide. Our calculator uses optimized formulas (sail × 4.0 + corrections for board width and weight) tested against materials from Starboard, K4, Tabou and other brands.

Use the "one-foot-off" rule (OFO): measure board width exactly 30 cm (1 foot) from the tail. This width is a standard starting point for fin length — the maximum fin length is roughly this width plus 2 cm, the minimum 6-10 cm less. The calculator uses this width as one of the input variables for a more accurate recommendation.

Low aspect = wider front wing, easier to lift, more stable — ideal for freeride and beginners. Mid aspect = balance between lift and speed, suited for allround and freestyle. High aspect = long narrow wing, high top speed, efficient glide — designed for racing, downwind and advanced freeride. The calculator shows all three so you can pick what suits your riding style.

Wave fins are significantly shorter than freeride and slalom. For a 75-85 kg rider with a 4.5-5.5 m² wave sail, the right length is 18-24 cm. Single-fin setups go slightly longer; thruster/quad setups use shorter fronts (12-16 cm) plus smaller sides. For wave fins, profile and stiffness matter almost more than length: softer profiles give more drive through the turn.

A weed fin has a strongly raked-back profile, designed to shed plant material rather than catch on it. Use it on spots with weed, grass or shallow sandy water — common on inland waters in the Netherlands, German Baltic, French lakes in summer, and Florida flats. A weed fin moves the center of effort backwards, so move your mast base and footstraps slightly back too for proper balance.

For slalom and freeride, a weed fin is roughly 18% shorter than a regular fin with comparable performance (due to greater surface area per cm of length). For wave and freestyle: 10% shorter — shorter fins have relatively less surface-area difference. The calculator applies this automatically when you enable the weed fin toggle.

For beginners: a shorter mast (60-75 cm) keeps you closer to the water — less daunting and softer touch-downs. Intermediate: 75-85 cm for more room to correct height. Advanced: 85-95 cm for downwind and choppy water — less risk of breaching. Also consider water depth at your spot: a 90 cm mast won't work in 1 m of water. The calculator shows a mast recommendation per level in the foil setup block.

G10 (fiberglass-epoxy laminate) is thicker, more forgiving, cheaper and excellent for freeride and beginner slalom. Carbon is thinner, stiffer, faster and lighter — but less forgiving in choppy water. The calculator provides both sizes because a carbon fin can typically be about 5% shorter than G10 for comparable performance (MUF X-Ride vs Ride benchmark).

Yes. The formulas are validated against extensive market benchmarks — materials and publications from Starboard, K4, Tabou, F-One, TAAROA, Ketos, MUF, SROKA and MACkite, plus public fin guides from PWA pro Nico Prien (NP7) and the Bornhoft/RYA fin studies. As long as you select the correct discipline and style, the calculator provides brand-agnostic recommendations that translate 1-to-1 to any manufacturer's lineup.