Estimate expected RTK GPS horizontal and vertical accuracy from base-to-rover distance, PDOP, and operating mode (Fixed/Float/Static). Plan your GPS setup for grade control, staking, and survey work. Actual accuracy may vary based on multipath, atmospheric conditions, and equipment.
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Shop Express Tools →RTK GPS accuracy is not a fixed number — it is a budget composed of several error sources. The dominant factors for construction use are: (1) baseline distance (atmospheric errors decorrelate), (2) satellite geometry (PDOP), (3) multipath from reflective surfaces near the antenna, and (4) equipment quality. This calculator addresses baseline distance and PDOP — the factors you can assess in the field. Multipath and atmospheric conditions require judgment and site-specific assessment.
The most important status check on any RTK system is Fixed vs. Float. In Fixed mode, the receiver has resolved the integer ambiguity in the carrier-phase measurement — this is what gives centimeter-level accuracy. In Float mode, ambiguity is estimated but not fixed — accuracy is typically 0.3–1.0 ft, suitable only for rough positioning. Many inexperienced GPS users do not realize their system is in Float and proceed with layout work at inadequate accuracy. Always confirm Fixed status before staking.
Network RTK services (Trimble VRS Now, Leica SmartNet, state DOT CORS networks) provide virtual base station corrections interpolated from a network of permanent reference stations. This allows RTK operation without setting up your own base, and effectively eliminates baseline distance error by providing a virtual base within a few miles. Accuracy is typically comparable to a local base at 5–10 miles. Check coverage for your state — most western and midwestern states have strong CORS network coverage.
| Application | Horizontal | Vertical |
|---|---|---|
| Grade control — subgrade | ±0.05 ft | ±0.05 ft |
| Finish grade — paving | ±0.03 ft | ±0.03 ft |
| Structure layout / staking | ±0.03 ft | ±0.05 ft |
| Topographic survey | ±0.1 ft | ±0.1 ft |
| Boundary / legal survey | ±0.02 ft | ±0.05 ft |
| GIS / asset mapping | ±0.5 ft | ±1.0 ft |
| Rough grading / cut-fill | ±0.1 ft | ±0.2 ft |
General industry guidelines. Actual project requirements may differ — always refer to project specifications.
RTK (Real-Time Kinematic) GPS is a differential GPS technique that uses a base station at a known position to correct rover measurements in real time. In Fixed mode with a short baseline (< 5 miles), RTK typically achieves horizontal accuracy of 0.03–0.05 ft (10–15 mm) and vertical accuracy of 0.05–0.1 ft (15–30 mm). Accuracy degrades with distance from the base station, higher PDOP (poor satellite geometry), and atmospheric disturbances. Actual accuracy may vary based on multipath, atmospheric conditions, and equipment quality.
PDOP (Position Dilution of Precision) is a dimensionless measure of satellite geometry quality. A low PDOP means satellites are spread across the sky — ideal for accuracy. PDOP < 2 is excellent; 2–4 is good for most work; 4–6 is marginal; > 6 is poor and precision work should be postponed. PDOP is shown on your GNSS receiver's status screen. It changes throughout the day as satellites move and varies by location due to obstructions (trees, buildings).
Most RTK systems maintain Fixed solution reliability within 20–30 miles. Beyond this, ionospheric and tropospheric errors decorrelate between base and rover, and maintaining Fixed lock becomes difficult. For precision grade control (< 0.05 ft accuracy), keep the baseline under 10 miles. For general staking and layout (< 0.1 ft), 20–25 miles is workable with good conditions. Network RTK (VRS) through services like CORS networks can extend effective range by using virtual base stations closer to your location.
RTK Fixed means the receiver has resolved the integer ambiguity in the carrier phase signal — this is the high-accuracy mode with centimeter-level precision. RTK Float means ambiguity is not fully resolved — accuracy degrades to decimeter level (often 0.3–1.0 ft), making it unsuitable for precision staking or grade control. Always wait for Fixed lock before beginning precision work. Float status may appear when the satellite constellation is weak, the baseline is long, or signal obstructions are present.
For best RTK performance: (1) Set base over a known control point whenever possible and enter the published coordinates — this eliminates base position error from the accuracy budget. (2) Avoid locations near metal structures, buildings, or trees that cause multipath. (3) Set base antenna as high as practical (tripod + pole) to improve satellite visibility. (4) Check PDOP before beginning work — avoid surveying when PDOP > 4. (5) Always perform a check shot on a known control point before beginning layout. (6) Document base position coordinates, setup time, and PDOP in your field notes.
Distance from base station to rover
From GNSS receiver display (ideal < 2.0)
Integer ambiguity resolved — highest accuracy
Typical RTK Accuracy by Baseline Distance (PDOP < 2, Fixed)
| Base-to-Rover Distance | Horizontal (typical) | Vertical (typical) | Use Case |
|---|---|---|---|
| < 5 miles | 0.03–0.05 ft (10–15 mm) | 0.05–0.1 ft (15–30 mm) | Grade control, staking, layout |
| 5–15 miles | 0.05–0.1 ft (15–30 mm) | 0.1–0.2 ft (30–60 mm) | General staking, topographic survey |
| 15–30 miles | 0.1–0.2 ft (30–60 mm) | 0.2–0.4 ft (60–120 mm) | Rough positioning, GIS, mapping |
| > 30 miles | 0.2–0.5+ ft (60–150+ mm) | 0.4–1.0+ ft | Not recommended for precision work |
Accuracy estimates are approximate and assume good satellite geometry (PDOP < 2), clear sky, and survey-grade GNSS equipment. Actual performance depends on equipment, environment, and atmospheric conditions.