Zerdly

Coordinate Precision Estimator (Decimal Places to Metres)

Converts latitude/longitude decimal places into ground resolution in metres on the WGS84 or GRS80 ellipsoid — the precision a coordinate is written to, not its accuracy.

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How to use this calculator

Inputs

How far one unit in the last decimal place of a decimal-degree coordinate is on the ground — or how many decimals a target resolution needs.

Decimal degrees (−31.95), DMS (31 57 0 S) or DDM (31° 57.0′ S).

Enter the values and press Calculate.

Or load an example to see a worked result.

One step in the last decimal place
Proportional
One step in the last decimal placeA rectangle one decimal step wide (east) and one step tall (north), with the rounding point at its centre and the half-step to a corner.east 1.11319 mnorth1.10574 m5 decimal places
Each extra decimal place divides the step by ten. The step is a representation limit, not measurement accuracy.

Batch from CSV

One row per calculation, with a header row. Values use the units currently selected in the form above. Up to 10,000 rows; nothing is uploaded.

How the method works

A fixed worked example to explain the method — it is not your result.

Representation step is not measurement accuracy
Illustrative method
Representation step is not measurement accuracyA rectangle one decimal step wide (east) and one step tall (north), with the rounding point at its centre and the half-step to a corner.east 1.11319 mnorth1.10574 m5 decimal places
Each extra decimal place divides the step by ten. The step is a representation limit, not measurement accuracy.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Choose decimal places → ground resolution, or a target resolution → decimal places needed.
  2. Enter the latitude and the number of decimal places (or the target in metres).
  3. Choose the measure: one step, the rounding error per axis (half a step) or the worst-case corner error, and the ellipsoid.
  4. Press Calculate.

How it works

One unit in the d-th decimal place of a latitude spans M·π/180·10⁻ᵈ metres, where M = a(1 − e²)/(1 − e² sin²φ)^{3/2} is the meridional radius of curvature.

For longitude it is N·cos φ·π/180·10⁻ᵈ, with N = a/√(1 − e² sin²φ). It shrinks towards the poles and is zero at them.

Rounding to d places can move a point by half a step on each axis, and by √(half² + half²) at worst.

These figures describe how finely a coordinate is WRITTEN. They are not the accuracy of the measurement behind it.

Worked example

5 decimal places at the equator, WGS84. Latitude step 1.10574276 m, longitude step 1.11319491 m, worst-case rounding error 0.785 m. At Perth (−31.95°) the longitude step falls to 0.945 m while the latitude step rises to 1.109 m.

Common mistakes

  • Treating 8 decimal places as millimetre accuracy. A phone GNSS fix is still metres.
  • Using 111.32 km for a degree of latitude everywhere: it is 110.574 km at the equator and 111.694 km at the poles.
  • Forgetting that longitude steps shrink with latitude.

Frequently asked questions

How many decimals do I need?

5 places ≈ 1 m, 6 places ≈ 0.1 m. More than that rarely helps unless you have survey-grade GNSS.

Related tools

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Cite this tool

Zerdly. (2026). Coordinate Precision Estimator (Decimal Places to Metres). Retrieved from https://www.zerdly.com/tools/coordinate-precision-estimator-decimal-places-to-metres/

Tip: Enter any known values to calculate the remaining results.

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