Is GPS speed more or less accurate than GPS position?

Often more accurate at useful speeds. Many GPS chips calculate speed from the Doppler shift of the satellite signals, which can be more precise than deriving speed from the change in position between two fixes, especially when position accuracy is temporarily degraded.

Why does accuracy get worse at low speed?

At very low speeds, position "jitter" (small random variation between fixes) becomes a larger fraction of the actual movement, which is why speedometers — including this one — treat very low speeds as effectively stationary rather than reporting noise as motion.

Can weather affect GPS accuracy?

Heavy weather has only a minor direct effect on civilian GPS signals. The bigger factors are what's between your device and the open sky — buildings, terrain, and dense tree cover — and how many satellites are in a good geometric spread above you.

Guides

How Accurate Is GPS Speed?

What determines GPS speed accuracy: satellite geometry, signal obstruction, device hardware, and how speed readings differ from position accuracy.

What affects GPS accuracy

Consumer GPS accuracy depends on several factors working together: how many satellites your device can see, how they're distributed across the sky (a cluster of satellites in one part of the sky gives a worse fix than a wide spread), and whether anything is blocking or reflecting the signal before it reaches your antenna.

Multipath interference — where a signal bounces off a building or other surface before reaching your device — is one of the most common sources of error in cities. Dense tree cover and being indoors can block signals outright, reducing the number of satellites available and widening the reported accuracy radius.

Speed accuracy versus position accuracy

It's worth separating two related but different numbers: how precisely your device knows where it is (position accuracy, usually reported as a radius in meters) and how precisely it knows how fast it's moving (speed accuracy). Many modern GPS chips report a speed value directly, derived from the Doppler shift in the satellite signal, which tends to be more stable than calculating speed by measuring the distance between two consecutive positions and dividing by time — particularly at lower speeds, where position noise has a larger relative effect.

This is why a speedometer tool should prefer a device-reported speed value when available, and only fall back to a position-difference calculation when it isn't — which is how SpeedCheck's tracking works under the hood.

What you can do about it

Use the device outdoors with a clear view of the sky.
Give it a few seconds after starting — the first fix after opening the app is usually the least accurate one.
Avoid relying on readings taken in tunnels, parking garages, or dense urban canyons between tall buildings.
Treat reported accuracy (shown as ±X meters) as a guide: smaller numbers mean the device is more confident in the fix.

Frequently asked questions

Is GPS speed more or less accurate than GPS position?: Often more accurate at useful speeds. Many GPS chips calculate speed from the Doppler shift of the satellite signals, which can be more precise than deriving speed from the change in position between two fixes, especially when position accuracy is temporarily degraded.
Why does accuracy get worse at low speed?: At very low speeds, position "jitter" (small random variation between fixes) becomes a larger fraction of the actual movement, which is why speedometers — including this one — treat very low speeds as effectively stationary rather than reporting noise as motion.
Can weather affect GPS accuracy?: Heavy weather has only a minor direct effect on civilian GPS signals. The bigger factors are what's between your device and the open sky — buildings, terrain, and dense tree cover — and how many satellites are in a good geometric spread above you.