Map Tile Zoom Resolution Calculator
Slippy maps split the world into tiles at integer zoom levels. The ground distance a single pixel covers, the resolution, halves each time you zoom in and depends on your latitude because Web Mercator stretches toward the poles. This calculator returns metres per pixel, the map scale at a stated screen DPI, and the full-width tile span at any zoom level and latitude. Use it to choose a zoom level for a target detail or to label a map's scale.
Tile resolution formula
resolution = (cos(lat) * 2 * pi * R) / (tile size * 2^zoom)
R = 6,378,137 m (WGS84 equatorial radius)
map scale = resolution * dpi / 0.0254
tiles across = 2^zoom
The world circumference at the equator is 2 times pi times R. Dividing by the total pixel width (tile size times 2 to the zoom) gives equatorial metres per pixel, then the cosine of the latitude corrects to local ground resolution. Map scale converts metres per pixel to a representative fraction at the chosen screen DPI.
Worked example
Zoom 15, latitude 40 degrees, 256-pixel tiles. 2^15 = 32,768 tiles across, so 32,768 times 256 = 8,388,608 pixels wide. Equatorial resolution = 2 times pi times 6,378,137 / 8,388,608 = 4.777 m/pixel. Times cos(40) = 3.66 m/pixel, or 365.97 cm/pixel. At 96 DPI the map scale is about 1 : 13,833.
Tile resolution: frequently asked questions
What is ground resolution in web maps?
Ground resolution is the distance on the ground represented by one screen pixel. In the Web Mercator tile scheme used by most slippy maps, it depends on the zoom level and the latitude, shrinking as you zoom in and as you move away from the equator.
What formula gives metres per pixel?
resolution = (cos(latitude) * 2 * pi * R) / (tile size * 2^zoom), where R is the Earth's equatorial radius (6,378,137 m for WGS84), tile size is the pixels per tile (256 in the standard scheme), and zoom is the integer zoom level. This is the published Web Mercator ground-resolution formula.
Why does resolution depend on latitude?
Web Mercator stretches the map increasingly toward the poles. The cosine of the latitude corrects the equatorial resolution to the true ground distance per pixel at your location, so a pixel covers less ground near the poles.
What tile size should I use?
The classic slippy-map tile is 256 by 256 pixels, which is the default here. Retina or high-density tile sets use 512 pixels; set the tile size accordingly if your provider serves 512-pixel tiles.
Sources and references
- National Geospatial-Intelligence Agency: WGS84 equatorial radius.
- U.S. Geological Survey: map projection and scale reference.
- Formula: standard Web Mercator (EPSG:3857) ground-resolution geometry.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.