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GPS Accuracy Estimate Calculator

Work out gps accuracy estimate instantly with clear inputs, formula shown and shareable results.

About GPS Accuracy Estimate Calculator

Position error is the product of geometry and ranging error: sigma equals HDOP times UERE. Corrections attack the UERE term — SBAS removes most ionospheric error, DGPS removes local common-mode error, and RTK uses carrier phase to reach centimetres. Vertical error is typically 1.5-2 times horizontal.

Formula

GNSS accuracy

sigma_horizontal = HDOP x UERE; 95% accuracy is about 2 sigma

Worked example

With the default values below, GPS Accuracy Estimate Calculator returns Horizontal accuracy (1 sigma) of 0.0240. Change any input above and every figure here is recalculated in your browser.

Inputs used

HDOP
1.2
Ranging error (UERE)
4 m
Satellites tracked
9 sats
Correction typeone of Standalone GNSS, SBAS / WAAS, DGPS, RTK fixed
RTK fixed

Results

Horizontal accuracy (1 sigma)
0.0240 m
95% confidence accuracy
0.0480 m
Vertical accuracy estimate
0.0384 m
Correction applied
RTK - centimetre level with a fixed solution

Step by step

  1. 1Values used
  2. 2GNSS accuracy
  3. 3Horizontal accuracy (1 sigma)= 0.0240 m
  4. 495% confidence accuracy= 0.0480 m
  5. 5Vertical accuracy estimate= 0.0384 m
  6. 6Correction applied= RTK - centimetre level with a fixed solution

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What is HDOP?

A geometry factor: how well the tracked satellites are spread across the sky. Below 1 is excellent, 1-2 good, above 5 poor and usually caused by obstructions.

Why is vertical accuracy worse?

Satellites are only ever above the horizon, so there is no geometry below the receiver to constrain height as well as horizontal position.

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