Average wind, not gusts. Use the forecast’s mean wind for your session window; the gust figure would send you a size too small.
Every kite has one wind range where it is a pleasure and a wider one where it merely survives. This calculator finds the pleasant one: enter your weight and the average wind, and it names the size that fits, the band around it, and the right kite for every other wind speed you are likely to meet. It is aimed at beginner and intermediate suggestions. Experienced kitesurfers can size up one M per suggestion.
Find your kite size
Two inputs. Your weight, in kg or lb. And the average wind for your session, in knots, km/h or mph: the forecast mean, not the gust figure, because gusts are what your depower is for. The table underneath the result is the part worth a screenshot; it covers your weight across the whole range from 10 to 30 knots.
Two real sizes usually bracket the calculated ideal. The smaller one rides controlled: less pull in the gusts, a little more work in the lulls. The bigger one rides powered: planes earlier, pulls harder, asks more of your edge. Confident riders on small boards tend to take the bigger kite; anyone riding chop, or anyone still counting sessions, is better served by the smaller.
The maths
kite size (m²) = weight (kg) × 2.30 / average wind (knots)
Controlled edge of the band: factor 2.05. Powered edge: factor 2.55.
Worked example: a 75 kg rider in 18 knots gets 75 × 2.30 / 18 = 9.6 m². No factory makes a 9.6, so the calculator maps it onto the sizes that exist and offers the 9 and the 10, with the 10 as the headline because it sits closer. The same rider’s controlled edge is 75 × 2.05 / 18 = 8.5 and the powered edge 75 × 2.55 / 18 = 10.6, which is why the band around the answer spans roughly one size in each direction.
The factor 2.30 is not our invention. Published size calculators for a normal twintip freeride setup cluster between 2.1 and 2.4, and 2.30 sits in the middle of that consensus. It assumes a twintip of ordinary size, a tube kite of ordinary efficiency, and a rider who wants to cruise, go upwind and land the occasional jump.
If you have read the wind window page, you know kite power grows with the square of the airflow over the kite, so a straight weight-over-wind rule can look too simple. It is not. Apparent wind, board speed, how actively you fly the kite and how far you sheet out absorb most of that square term on the water, which is why the sizing charts schools and manufacturers actually publish follow roughly weight over wind. A squared formula produces sizes that are visibly wrong at both ends of the range.
Why the box quotes a much bigger range
A Duotone Evo SLS in 9 m is rated for roughly 14–34 knots. A Cabrinha Moto X Lite also in 9 m quotes about 15–34 knots for a 75 kg rider. Our calculator says the same 9 m is ideal for that rider at about 19 knots and sweet between roughly 17 and 21.
The manufacturer’s range is where the kite is usable: at the bottom end you can keep it in the air and slog home, at the top a skilled rider can still hold it down.
Meanwhile the sweet spot is where the kite is pleasant: enough power to plane early and drive upwind, enough depower in reserve that a gust is information rather than an event.
Rig for the sweet spot and treat the printed range as the outer fence, not the target. How the brands place those fences differs more in marketing than in physics.
What moves the answer
The weight-class chart on our equipment page brackets the same numbers into coarser bands; this list is what moves you around inside a band.
- Board size. A big twintip planes two or three knots earlier than a small one, which is worth about one kite size in light wind. Learners on large school boards get away with less kite than the formula says.
- Water state. Smooth water holds your board speed, and board speed feeds apparent wind, so you can carry the bigger kite. Chop scrubs speed off and rewards the smaller one.
- Gusts against the average. A day of 18 gusting 26 is not an 18-knot day. Size for something between the mean and the gusts, closer to the gusts the more nervous the wind, and remember that a rise from 15 to 21 knots roughly doubles the pull.
- Rider level. Experienced riders keep a kite working through lulls and can hold the powered end of the band. Newer riders should sit at the controlled end, where mistakes cost metres instead of crashes.
- Kite type. The formula assumes an ordinary tube kite. Light-wind specials and foil kites fly earlier and effectively shrink the number; wave kites built to drift and school kites built to forgive both trade grunt away.
The two honest edges
Below about 12 knots the formula stops being trustworthy, and the calculator says so on screen. A kite needs a minimum wind just to stay flying, and that minimum does not shrink with the rider, so the low end stops scaling with weight. Light riders in marginal wind should round up a size rather than down; the equipment page’s chart does exactly that for the lightest weight class. Down here, board size, kite efficiency and patience decide more than any number, and the size shown is a starting point for the beach conversation, not a verdict.
Above about 28 knots the calculator turns conservative for the opposite reason: mistakes scale with the wind squared even when sizing does not. Check the kite’s rated range, be honest about your level, and when two sizes both seem plausible, rig the smaller one. Strong-wind days reward riders who arrive with a plan and a small kite, not riders who negotiate with a big one.
The question behind the question: which kites to own
Nobody buys a kite for one forecast. When people ask what size they need, they usually mean: which two or three sizes cover most of my days? Run your own weight through the table above and the answer falls out. For a 75 kg rider it reads like this: a 12 m owns roughly 13 to 16 knots, a 9 m owns 17 to 21, and a 7 m takes 22 to 27. Two kites, the 12 and the 9, cover the big middle of a thermal season; the 7 is the strong-day addition. Around 60 kg the whole ladder slides one size down, around 90 kg one size up.
If you own only one kite, buy the middle rung for the wind your home spot serves most often, and rent the edges. And if you are still learning, do not buy anything yet: lessons include the full setup, and a rental fleet lets you ride three sizes in a week before you spend money on one.
A starting point, not the last word
This calculator is a well-calibrated first guess for a normal twintip and freeride riding. It does not know your board, your spot, today’s gust spread or your hours on the water. The manufacturer’s wind range, the local conditions and an instructor’s eye all outrank it, and kite sizing sits close enough to safety that they should. Use the number to arrive at the beach with the right expectation, then let the beach correct it.
Or get handed the right kite
Tell us your weight and we match a kite from the rental fleet to the day’s forecast at Sektor Rinia, Durrës. The lagoon is about one to two meters deep across a huge area, so changing down a size mid-session means just walking back, not swimming.