Lawn Area Calculator

The input every other calculator needs

Every TurfDial tool asks how big your lawn is. If that number is off — and “I think it’s about 5,000 square feet” usually is — every rate you calculate is off by the same factor. Apply product to 20% more area than you calculated because your estimate was low, and that error compounds across every tank mix, every fertilizer bag, every pre-emergent application. Trace the turf once, get the real number, carry it everywhere.

How it works

Use Use my location or manual pan and zoom to navigate to your property on the satellite map. Click Draw polygon and place vertices around the perimeter of your turf — click or tap to set each point, then double-click (or click the first vertex) to close the polygon. The area readout updates live as each vertex is placed.

If your lawn has multiple disconnected sections — a front yard and a back yard separated by the house, strips of turf on either side of a driveway — draw a separate polygon for each section. The areas are summed automatically. Finished polygons remain editable: drag any vertex to fine-tune the trace.

Methodology — geodesic polygon area

Map coordinates are WGS 84 latitude/longitude. Area is computed using @turf/area, which implements the Chamberlain–Duquette algorithm for geodesic polygon area on a sphere:

Robert G. Chamberlain & William H. Duquette, Some Algorithms for Polygons on a Sphere, JPL Publication 07-03, Jet Propulsion Laboratory, Pasadena, CA, 2007. trs.jpl.nasa.gov/handle/2014/40409

The algorithm computes a signed spherical excess for each edge of the polygon and sums them. It accounts for the curvature of the Earth, which matters even at residential-lawn scale — a flat-plane calculation can introduce a small but measurable error. Accuracy is well under 0.1% for any polygon a lawn tracer is likely to draw.

The result is returned in square meters. Unit conversions used:

1 m² = 10.7639 sq ft
1 acre = 43,560 sq ft

When the total exceeds 20,000 sq ft, the display switches to acres as the headline figure, with square feet shown as the secondary. The “Copy sq ft” button always copies the rounded integer square footage, regardless of display mode.

How to get an accurate trace

The tool’s accuracy is only as good as the polygon you draw. A few practices that help:

• Trace the turf edge, not the lot line. You want the area of grass, not the total parcel. Exclude the driveway, walkways, planting beds, hardscape, and the house footprint.
• Zoom in before tracing. Most satellite imagery is detailed enough at 18–20× zoom to distinguish turf from pavement or mulch. Tracing at a low zoom level introduces the most error.
• Use multiple polygons for complex shapes. A front yard, a back yard, and a side strip are each easier to trace accurately as separate polygons than as one irregular shape.
• Drag vertices to adjust after drawing. You don’t have to get it perfect on the first click — tap a completed polygon’s vertex to drag it into the correct position.

Honest caveats

• Area is only as accurate as the trace. A careful trace of the turf edge is accurate; a sloppy one isn’t. The algorithm can’t improve on the input.
• Satellite imagery has a capture date. The imagery may be months or years old. Recent construction, new beds, or additions may not be reflected.
• Parallax and angle. Satellite images are captured at a slight angle. Features with vertical extent — hedges, fences, structures — can appear shifted from their true ground position. Trace the ground edge, not the apparent top of a hedge.
• This is a planning estimate, not a survey. For legal, property, or commercial purposes, use a licensed surveyor.

Satellite imagery by MapTiler. Map data © OpenStreetMap contributors (ODbL). Geodesic area algorithm: Chamberlain & Duquette (2007), JPL Publication 07-03.