💨 True Wind Calculator
Enter the apparent wind speed and angle you read on deck plus your boat speed to get the true wind speed and true wind angle over the water.
🧭 Apparent Wind to True Wind
What is a True Wind Calculator?
It strips your own motion out of the wind. The wind your instruments feel — the apparent wind — is a blend of the real wind over the water and the headwind you make by sailing forward. Feed the calculator your apparent wind speed and angle and your boat speed, and it solves the wind triangle to hand back the true wind speed and the true wind angle.
Use it to pick the right sail and reef for the real conditions, judge whether a shift has come from the wind or from your own speed, and plan gybes and laylines in true-wind terms. Results assume steady flow and calibrated readings, so treat them as a working estimate and cross-check against the sea and sky.
❓ Frequently Asked Questions
What's the difference between apparent and true wind?
True wind is the wind you'd feel standing still — the actual air movement over the water. Apparent wind is what you feel on a moving boat: the true wind combined with the headwind created by your own motion. Sailing upwind the apparent wind reads stronger and further forward than the true wind; sailing downwind it reads weaker and further aft.
How does the calculator work out the true wind?
It treats the wind as a vector triangle. From your apparent wind speed (AWS), apparent wind angle (AWA), and boat speed (BS) it computes true wind speed as √(AWS² + BS² − 2·AWS·BS·cos AWA), and the true wind angle from the components of that triangle. The result is the true wind speed in knots and the true wind angle off the bow in degrees.
Where do I read the apparent wind angle from?
The apparent wind angle is the angle between the boat's bow and the wind you feel, from 0° (dead ahead) to 180° (dead astern), read off your masthead wind vane or instruments. Enter it as an angle off the bow regardless of tack — the geometry is the same to port or starboard.
Why does the true wind matter if my instruments feel the apparent wind?
Tactics and forecasting work in true wind: it tells you the real wind strength for sail selection and reefing, and the true wind direction for judging shifts, laylines, and where the next puff is coming from. Racing sailors and passage planners constantly convert apparent readings into true wind to make those calls.