True Wind Calculator

Resolve the wind triangle between a sailing boat's motion and the wind. Convert apparent wind (what the boat's instruments feel) into true wind over the water, or predict the apparent wind from a true-wind forecast and your course. Enter boat speed, the known wind speed and its angle off the bow (0° = headwind, 180° = dead downwind), and the tool returns the other pair. Upwind the boat's motion inflates the apparent wind and pulls it toward the bow; downwind the boat runs away from the wind, so the apparent is lighter and further aft than true. Pure arithmetic — a velocity-triangle solution with no leeway, current, gusts or instrument calibration. Everything runs locally in your browser.