GPS DOP Accuracy Calculator
GPS position accuracy depends on two things: how good the satellite geometry is, and how clean each range measurement is. Dilution of precision (DOP) captures the geometry as a single dimensionless multiplier, while the user-equivalent range error (UERE) captures the one-sigma error per satellite range. Multiply them and you get the expected one-sigma position error. This calculator takes your current HDOP, VDOP and UERE and reports the estimated horizontal, vertical and 3D position error, plus a 95 percent horizontal figure. UERE is a user-editable input because it depends on your receiver and conditions.
DOP position error formula
horizontal error = HDOP * UERE
vertical error = VDOP * UERE
PDOP = sqrt(HDOP^2 + VDOP^2)
3D error = PDOP * UERE
horizontal 95% (2DRMS) = 2 * HDOP * UERE
All error figures are one-sigma unless labelled 95 percent. The 2DRMS multiplier of 2 is the conventional approximation for the 95 percent horizontal radius. PDOP combines horizontal and vertical geometry.
DOP and accuracy context
- DOP is dimensionless: it scales ranging error into position error and is set by satellite geometry alone.
- Lower DOP is better; PDOP below 2 indicates excellent geometry.
- UERE depends on receiver quality, augmentation (SBAS, RTK) and atmospheric conditions, so it is user-editable.
- The GPS Standard Positioning Service is specified at 95 percent confidence, not one sigma.
- Obstructions, canyons and tree cover raise DOP by limiting which satellites are visible.
GPS DOP accuracy: frequently asked questions
What is dilution of precision (DOP)?
DOP is a dimensionless number that describes how satellite geometry amplifies ranging error into position error. Lower DOP means a better satellite spread and a more accurate fix. Common variants are GDOP (geometric), PDOP (position, 3D), HDOP (horizontal), VDOP (vertical) and TDOP (time).
How is position error estimated from DOP?
The standard relationship is position error equals DOP multiplied by the user-equivalent range error (UERE), the one-sigma ranging error per satellite. For example, an HDOP of 1.2 with a 4 m UERE gives an expected horizontal error of about 4.8 m (one sigma).
What is a good DOP value?
As a common field guide, a PDOP under 2 is excellent, 2 to 5 is good, 5 to 10 is moderate, and above 10 is poor. The exact thresholds depend on the application. DOP changes constantly as satellites rise and set, so it is a real-time quality indicator.
What is UERE?
User-equivalent range error is the combined one-sigma error in the pseudorange measurement to a single satellite, from clock, ephemeris, ionosphere, troposphere, multipath and receiver noise. It is an empirical figure that varies by receiver, augmentation and conditions, so it is a user-editable input here.
Why does the GPS Standard Positioning Service quote a number larger than this?
Specification accuracy figures are typically stated at 95 percent confidence, roughly two times the one-sigma value, and assume worst-case geometry. The DOP times UERE result is a one-sigma estimate for the current geometry. Multiply by about 2 for a 95 percent horizontal figure (2DRMS).
Official sources
- U.S. Government GPS information: gps.gov performance and accuracy.
- U.S. National Geospatial-Intelligence Agency: GPS and geodetic references.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.