A quick browser reading
Open the online speedometer, choose knots, press Start and allow location access. It needs a usable location reading and does not save trips in the iPhone app.
Try the browser speedometerBoat GPS Speedometer with Knots Display
See your boat’s GPS Speed Over Ground (SOG) in knots on your iPhone. Record trips and review basic speed and distance statistics.
SOG describes movement over the ground. It can differ from speed through the water because of currents. GPS Speedometer does not measure Speed Through Water (STW) or calculate Velocity Made Good (VMG).
Choose the tool for your trip
Record trips in the iPhone app
Use the native app for GPS speed and saved trip summaries. Core recording and basic summaries are free; detailed analysis and sharing require PRO.
See free and PRO featuresNeed another marine measurement?
For speed through water, VMG or navigation, choose equipment or software that provides those functions. This app is a supplementary SOG display.
Understand the measurementsGPS Speedometer on a boat
Real photos of the app in use, with km/h selected. Knots and MPH are also available in the unit settings.
SOG, STW and VMG measure different things
A GPS reading tells you how fast you are moving over the ground. Choose the measurement that matches the question you want to answer.
- SOG
- Speed Over Ground: speed relative to the Earth’s surface. This is the GPS speed shown by the app.
- STW
- Speed Through Water: speed relative to the surrounding water. The app does not measure it.
- VMG
- Velocity Made Good: the component of velocity along a chosen direction, such as toward a waypoint. The app does not calculate it.
A following current changes SOG
5 knThrough water
+ 2 knFollowing current
= 7 knOver ground
1 knot is 1 nautical mile per hour, exactly 1.852 km/h.
Read the SOG and STW guideWhat the iPhone app includes
Use the free core features to check speed and keep a basic trip record. Choose PRO when you need its additional tools.
Free core features
- GPS speed in knots, MPH and km/h
- Current, maximum and average speed, plus distance
- Trip recording, saving and basic saved-trip summaries
Optional PRO features
- Detailed route playback and saved-trip charts and analysis
- GPX export and trip sharing
- Picture-in-Picture speed display over other apps
PRO is available by subscription or one-time purchase; both unlock the same PRO features. Check Apple’s purchase screen for your region’s current price.
Set up the iPhone app before departure
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Choose knots
Download GPS Speedometer and select knots in the app’s speed-unit settings.
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Allow location and secure the phone
Enable location access, including Precise Location where available. Use a suitable mount and keep a clear view of the sky. Wait for a usable reading.
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Start a trip recording
Start recording when you want to save the trip. Afterwards, open the saved trip for its basic summary; detailed playback and charts require PRO.
Conditions that affect the reading
Location and reception
Location permission and usable data are required. Obstructions, low speed and device processing can affect the reading.
Offline core tracking
The native app’s GPS speed and trip recording work without internet when location access and a usable GPS signal are available. Maps and connected features may be unavailable offline; weather requires PRO and internet.
Phone, mount and power
Follow the device, case, mount and charger manufacturers’ instructions. Plan for water exposure, heat and battery use, and position the display without obstructing other equipment.
Boat speedometer questions
Does the app show speed over ground or through water?
It shows GPS Speed Over Ground (SOG), including knots. It does not measure Speed Through Water (STW) or calculate Velocity Made Good (VMG).
Which features are free?
Core GPS speed, units, maximum/average speed, distance, trip recording, saving and basic summaries are free. Detailed route playback, charts, GPX sharing and Picture-in-Picture require PRO.
Can I record a trip without mobile coverage?
Yes, the native app’s core speed and trip recording work without internet, with location permission and a usable GPS signal. Maps may be unavailable offline. Weather requires PRO and internet.
Can a recording continue when I leave the app?
GPS can continue while a trip is actively being recorded or Picture-in-Picture is in use. PiP requires PRO. When recording ends, open the saved trip to view its basic summary.
Can it replace marine instruments or navigation equipment?
Use it as a supplementary SOG display. No fixed precision or superiority to another instrument is guaranteed. Use suitable equipment or software for STW, VMG, navigation or dedicated racing analysis.
Can I check boat speed without downloading the app?
Use the separate browser speedometer: choose knots, press Start and allow location access. It needs a usable location reading. It does not save trips in the native app; use the iPhone app to record and review them.
Keep a record of your next boat trip
Download GPS Speedometer for iPhone for SOG in knots and free basic trip summaries.
Free download · Optional PRO subscription or one-time purchase
GPS Speedometer is a supplementary speed and trip tool. It does not replace marine navigation equipment, charts or instruments required for your vessel.