CoordCalc is a set of fifteen calculators and twelve guides for the arithmetic that surrounds a survey: coordinate conversions, distances and areas, units and land records, slope, scale, curves and traverses. It is free, it runs entirely in your browser, and it is written for the person who needs a number they can defend — a surveyor checking a plan, a student working through a problem, an engineer reading a CAD file, a GIS technician untangling a datum.
Most coordinate questions are not hard mathematics; they are hard bookkeeping. Which datum, which zone, which foot, which of the three codes that look the same but are not. The web has plenty of converters that return an answer and nothing else, and the failure mode is always the same: a confidently wrong number that nobody questioned because a website produced it.
So each calculator here does two things. It computes, and it explains what it assumed — the ellipsoid, the false origin, the unit convention, the difference between the two feet, the reason a projected area is not a ground area. The guides go further and cover the questions that come up around the arithmetic: how to read a UTM reference, why an MGRS round trip lands a metre away, what a geoid is doing under an ellipsoid, why the US survey foot took until 2023 to die.
One shared geodesy library sits behind every tool. It is plain JavaScript with no dependencies and no network access, and it is written the cautious way: the transverse Mercator projection uses the published series, the inverse is solved by Newton iteration against that same series rather than by a truncated reverse formula, distances use Vincenty's inverse on the WGS84 ellipsoid with a spherical fallback for near-antipodal pairs, and the Norway and Svalbard zone exceptions are applied rather than ignored.
The library is measured, not trusted. Against PROJ — the reference implementation behind pyproj and QGIS — the UTM easting agrees to better than 0.1 mm and the northing to better than 0.9 mm across test points from the equator to 78° N, and a forward-then-inverse round trip closes to a few nanometres. The EPSG code lookup is generated programmatically from the EPSG registry itself rather than typed in, so its names, units, areas of use and projection parameters are the registry's own. The developer guide quotes the exact figures and shows how to reproduce them in a browser console.
The same discipline applies to the tests: every calculator is exercised in a real browser document against known values before it ships, and the batch converters are checked against hand-verified coordinate lists rather than against themselves.
The pages are hand-written HTML, CSS and JavaScript with no framework and no build step, which
keeps them small enough to load on a phone in the field and simple enough to work offline once
open. There is no login, no upload, no advertising and no cookie; the
privacy policy is short because there is almost nothing to report.
The calculators are also embeddable: any of them can be dropped into another page or an
intranet with embed=1, which is documented with the rest of the
URL and JavaScript API.
Every page states its assumptions and its limits, and every calculator carries the same reminder in its footer: results are for reference, and anything that governs a boundary, a construction line or a payment must be verified by a licensed professional under the standard that applies. That is not a legal formality bolted on for protection — it is the honest description of what a web calculator is.
Where a convention could go either way, the page says which way it went. Where a number is rounded for display, the page says the calculation used full precision. Where two authorities disagree — the two feet, the two Mercators, the geoid and the ellipsoid — the disagreement is the subject of the page rather than a footnote.
The site carries no advertising, no affiliate links and no sponsored content, and there is no paid tier. If that ever changes it will be said here first, plainly.
Wrong answer, unclear explanation, a unit or a projection you need that is missing — all of those are worth hearing about, and corrections are fixed rather than argued. The most useful report includes the input, the output you expected with its source, and the tool you used.
Suggestions for new tools are welcome too, particularly the tedious ones: the calculators that exist here began as someone's repetitive spreadsheet job.
CoordCalc publishes free surveying and coordinate calculators. Results are for reference — confirm against the governing standard before construction or procurement. About · Privacy & cookies · Terms of use · Developers