Boat Speedometer
SpeedCheck needs your device's location to measure speed. Your browser will ask for permission when you tap Start Tracking — your location is never stored or sent anywhere.
Do not interact with this device while driving. Have a passenger operate it, or mount it securely and glance only when safe to do so.
GPS speed on the water
This page defaults to knots, the standard marine speed unit, though you can switch to km/h or mph if you prefer. Mount your device securely and keep it dry — phones aren't rated for water exposure, so this is best used with proper waterproof protection aboard.
Because GPS reports speed-over-ground, expect some difference from a boat's built-in knotmeter in areas with current or tide — see the guide on GPS versus vehicle speedometers for how that comparison works in general.
Other speedometers
Related guides
Frequently asked questions
- Is this speed-over-ground or speed-through-water?
- GPS measures speed-over-ground — your actual movement relative to the Earth. A paddlewheel or impeller knotmeter measures speed-through-water instead. The two will differ whenever there's current or tide, since GPS includes the effect of the water moving under you.
- Why does my speed change without touching the throttle?
- Current and tide add to or subtract from your GPS speed-over-ground even at a constant engine output. This is normal and is one of the main reasons GPS and knotmeter readings disagree.
- Does it work far from shore?
- GPS reception doesn't depend on proximity to land — it depends on a clear view of the sky. Open water typically gives excellent GPS accuracy since there's nothing to block or reflect the signal.