About Draw a Radius

Draw a Radius is run by a single independent builder as six free map tools built around one idea: show the math, not just the number. Every tool states the formula it runs, works a real example through with the tool's own defaults, and shows exactly where a figure comes from -- the exact Earth-radius constant behind every distance, and the exact unit-conversion constant behind every mile, kilometer, acre or hectare.

How the tools work

Every tool on this site -- the radius drawer, the distance calculator, the mile-radius rings, the coordinates converter, and the area calculator -- routes its geometry through one shared set of pure functions, rather than each tool re-implementing its own math. Every formula is checked against a hand-derived expected value in the site's own test suite before it ships.

Where the map and the figures come from

Map tiles are © OpenStreetMap contributors, used under the OSM tile usage policy -- see the OSM tile usage policy for what that requires of us (attribution, no bulk downloading, no prefetching) and what it would require if this site's traffic ever grows heavy enough to need a paid tile provider instead. Address search uses OpenStreetMap Nominatim, rate-limited on our end to one request per second per its own usage policy. Straight-line distance uses the haversine formula on a sphere of radius 6,371.0088 km -- the WGS-84 mean radius, cited on the Distance Between Two Points page. Unit conversions (miles, nautical miles, acres, hectares) use exact international definitions, not rounded approximations.

What it doesn't do

Nothing on this site calculates driving distance, drive time, or a route of any kind -- every distance and every radius is a straight-line, as-the-crow-flies geometric estimate. Polygon and ring areas are computed from the coordinates you give the tool, not surveyed, and shouldn't be used for a legal property boundary, a construction plan, or any decision where a survey-grade measurement is required. See Terms.

Every tool

• Draw a Radius on a Map -- Click the map or search an address to set a centre, enter a radius in miles or kilometers, and draw up to five circles with area, circumference and a shareable link.
• Distance Between Two Points -- The as-the-crow-flies great-circle distance between two points in miles, kilometers and nautical miles, plus the initial compass bearing, computed with the haversine formula.
• Circle on a Map -- Draw a circle on a map for a delivery area, service radius or commuting range, with the same engine as the homepage tool and worked examples for common use cases.
• Mile Radius Map -- Preset rings at 1, 5, 10, 25, 50 and 100 miles around a chosen centre, with a computed table of each ring's area, so you don't have to type a radius by hand.
• Coordinates Converter -- Convert latitude and longitude between decimal degrees and degrees-minutes-seconds, with validation and a map jump to see what's at those coordinates.
• Map Area Calculator -- Click up to 30 points to trace a polygon on the map and get its area in acres, hectares, square kilometers and square miles, plus its perimeter.

Corrections

If a figure or citation here is wrong or out of date, email hello@drawaradius.com.