Sailing Speed Calculator (VMG)

VMG stands for Velocity Made Good — it's the component of your boat speed that is directed straight toward your destination (usually directly upwind or downwind). Even if your boat is moving fast, a poor angle can mean very little VMG. Maximising VMG means balancing speed and angle so you make the most ground toward your mark per unit of time.

VMG is calculated using the formula: VMG = Boat Speed × cos(True Wind Angle). For upwind sailing, a smaller TWA (sailing closer to the wind) increases the cosine value but usually reduces boat speed — the optimal VMG angle balances these two factors. For downwind sailing, the same principle applies but in the opposite direction.

Upwind VMG measures how fast you are progressing directly into the wind, while downwind VMG measures progress directly away from the wind toward a leeward mark. For upwind sailing, you typically tack at angles of 35–50° to the true wind. Downwind, sailing at around 140–160° TWA often gives better VMG than sailing dead downwind at 180°.

Sailing dead downwind (180° TWA) minimises your apparent wind, reducing boat speed significantly — especially in light air. Gybing at angles of around 140–160° TWA generates more apparent wind and therefore more boat speed, and the VMG toward the leeward mark is often better than going straight downwind. This is why top-level racers sail deep angles with frequent gybes.

Cross-track speed is the component of your boat speed that is perpendicular to your target direction — essentially speed wasted going sideways rather than toward your mark. It is calculated as Boat Speed × sin(True Wind Angle). While some lateral movement is unavoidable when tacking or gybing, minimising cross-track speed while maximising VMG is the goal.

Your optimal VMG angle depends on your polar speed curve — how fast your boat goes at each wind angle. In practice, you can experiment by pinching up or bearing away slightly and watching your VMG readout. This calculator lets you compare your current angle to a target angle so you can identify which gives better VMG with your actual boat speed data.

Standard VMG calculations do not factor in the distance and speed lost during tacks or gybes. In a real race, excessive tacking costs time even if the VMG angle is theoretically optimal. GPS chartplotters and race instruments that display VMG also typically ignore tacking losses, so tactical judgment is still needed alongside raw VMG numbers.

Most modern sailing instruments and GPS chartplotters — including Garmin, B&G, and Raymarine units — can display VMG in real time. Smartphone apps like SailTimer and various polar analysis tools also calculate VMG from GPS speed and compass heading. For racing, dedicated instrument systems often include polar target VMG so you can compare your actual VMG to the theoretical best.