How We Calculate Distances Between Cities
Start with an official coordinate
A distance is only as trustworthy as its endpoints, so every calculation on this site begins with the internal point â a latitude and longitude â published for each place in the U.S. Census Bureau Gazetteer files. The Gazetteer is a public, citable source, which means any reader can find the same coordinate we used and repeat our arithmetic exactly. We use the place's internal point rather than a postcode centroid, a commercial pin or a hand-picked map click, because the internal point is defined consistently for every city in the country, and consistency across thousands of pairs matters more than any individual pin's charm.
The haversine formula, in plain language
Given two latitude-and-longitude points, the straight-line distance between them is the great-circle distance: the length of the shortest arc over a sphere. The haversine formula computes that arc while handling the Earth's curvature correctly, unlike a flat-map measurement, which stretches distances badly over hundreds of miles. We use a mean Earth radius of 3,958.8 miles and round results to the nearest whole mile, because the inputs do not justify false decimal precision. The formula is deterministic â the same two coordinates always produce the same answer â which is precisely what a reference site needs: no traffic model, no routing preference and no commercial interest sits between the coordinates and the published figure.
Routing for the driving figure
Where a pair page says its driving distance was measured via OpenStreetMap routing, the figure came from OSRM, the Open Source Routing Machine, run against OpenStreetMap road data. OSRM assembles the fastest routable path between the two Census coordinates across the real road network and returns its length and an estimated duration, and where the engine provides a route summary naming the principal roads, we publish that summary with the figure. Where no measured route is published for a pair, the driving figure is an estimate â straight-line distance multiplied by a circuity factor of 1.25, with drive time at an assumed 50 mph average â and it is labelled an estimate in the headline, in the table and in the text, so a reader never has to guess which kind of number they are looking at.
Rounding, updates and corrections
Figures are retrieved and generated for the October 2026 edition of the site, and the source line on every page says so. Road networks change slowly and Census coordinates change more slowly still, but both do change: a new bypass can shorten a corridor, and a revised Gazetteer file can move an internal point slightly. When we refresh the data we regenerate the affected pages rather than patching numbers by hand, so the headline figure, the comparison table, the hub tables and the frequently asked questions can never drift apart from one another. If you believe a figure on this site is wrong, the contact page explains how to send a correction with the pair, the figure and your source, and we would rather fix a number than defend it.
Keep Exploring
Put the ideas on this page to work in the distance index, browse the New York hub or the Los Angeles hub for full tables, or read how we calculate every figure we publish. Each pair page applies the same method, labels measured routes and estimates differently, and names its sources, so the numbers you plan with are the numbers you can check.
Sources: Coordinates: U.S. Census Bureau Gazetteer files; driving data: OpenStreetMap/OSRM â retrieved October 2026.