Check a converted coordinate step by step
Verify the location, axes and projection before trusting a converted number.
Preserve the original
Keep a copy of the original coordinate together with its stated reference system, units and axis order. Work on a separate copy. Otherwise a mistaken conversion can be hard to distinguish from the source data later.
Check the location on the map
Look for a plausible country, region and landmark. A point in the wrong hemisphere or far outside the expected area suggests a unit, axis or reference-system problem. A point near the expected location still needs a more detailed check when accuracy matters.
Check axes and zone
For WGS84, enter longitude in X and latitude in Y. For projected systems, this form expects easting in X and northing in Y. Verify the exact SWEREF or UTM zone, not just the family of systems. Do not keep trying systems until a point merely looks close.
Convert back
Convert the result back to the original system and compare it with the saved input. A small round-trip difference is a useful consistency check, but both directions can share the same mistaken assumption. Our six-location WGS84/SWEREF test measures this round-trip behaviour with the public tool's rounding; it is not an independent survey control.