How many decimal places do GPS coordinates need to be accurate?

The short answer

Five decimal places is roughly a metre of resolution, and six is roughly ten centimetres — past that point a coordinate is recording precision no consumer GPS receiver can actually deliver. A GPX file usually stores six or more digits anyway, not because they are meaningful on their own, but because rounding them off buys nothing and can quietly cost something later. The digit count describes how the number is written down, not how accurately the phone knew where it was standing.

What each decimal place actually buys you

Latitude and longitude are measured in degrees, and a degree is a fixed, enormous distance — about 111 kilometres at the equator for a degree of latitude. Each digit after the decimal point divides that distance by ten, which is why moving from one decimal place to the next feels so dramatic:

• 1 decimal place ≈ 11.1 km — separates one town from the next
• 2 decimal places ≈ 1.11 km — separates one neighbourhood from the next
• 3 decimal places ≈ 111 m — separates one block from the next
• 4 decimal places ≈ 11.1 m — separates one building from the next
• 5 decimal places ≈ 1.1 m — roughly a single stride
• 6 decimal places ≈ 11 cm — finer than any consumer GPS receiver can actually place you

Longitude works the same way, but the real-world distance behind a degree shrinks the further a point is from the equator, since lines of longitude converge toward the poles. The table above holds closely for latitude everywhere, and for longitude near the equator — further out it is a useful approximation rather than an exact conversion.

Why a GPX file keeps all of them anyway

If a phone's GPS receiver is only accurate to a few metres, storing coordinates down to eleven centimetres looks like padding — and in one sense it is. But the extra digits are not costing anything meaningful: they are a handful of characters in a plain text file, and trimming them back to something that feels "reasonable" does not make the underlying reading any more or less accurate. It just discards information that was already there.

There is a real cost to rounding too aggressively, and it shows up in calculations rather than in storage. Distance is worked out by summing the gap between thousands of consecutive points; elevation gain is built the same way, point to point. Round every coordinate to four decimal places before doing that arithmetic and a small, consistent error gets introduced at every single point — one that does not cancel out, because it accumulates across the length of a hike. Keeping the coordinate at full precision and only rounding the final answer, if at all, avoids that.

Decimal places are not the same thing as accuracy

None of this means a phone actually knew its position to eleven centimetres. The number of digits after the decimal point describes how the coordinate is written down, not how good the fix was that produced it. A receiver with several metres of real-world uncertainty will still report a latitude and longitude out to six or seven decimal digits — the extra precision is simply how the number is represented, not a claim about the fix behind it. What actually determines how close that number is to where someone was standing is the receiver hardware, the satellite geometry at the time, and what stood between the phone and open sky — a separate question entirely from how the coordinate is formatted.

Where it actually matters

The practical case where decimal places matter is editing or comparing raw files by hand. Open a GPX in a spreadsheet, and it is tempting to round the latitude and longitude columns down to something that looks tidier — four or five decimal places instead of seven. Do that and re-export, and the track shifts slightly at every point, usually by less than the width of a trail, but enough that overlaying it against the original produces a line that does not quite retrace itself.

The same logic explains why two apps' exports of what should be the same hike do not always line up point for point. If one app rounds more aggressively than the other on export, the coordinates will not match exactly even when both recorded the same walk — a formatting difference, not a sign that one track is more accurate than the other.

Things that trip people up

• Assuming more decimal places means a more accurate GPS fix — the digit count is how the number is written, not a measurement of how good the fix was.
• Rounding coordinates in a spreadsheet to make a file look cleaner — this shifts the track slightly, and the original digits cannot be recovered once they are gone.
• Expecting two apps' exports of the same hike to overlay exactly, coordinate for coordinate — different rounding alone can explain a small mismatch, without either track being wrong.
• Treating six decimal places as proof of centimetre accuracy — it is a ceiling on how the number could be represented, not a floor on how well the receiver actually performed.

Where TrailCam fits in

TrailCam records each point at the precision the iPhone's GPS receiver reports and exports it unrounded, as GPX 1.1 or as CSV, so a route out of the app is the same set of numbers that were recorded on the trail rather than a version tidied up afterwards. Export is part of the optional TrailCam Pro upgrade; the app itself is free to download.