Lawn area calculator
Work it out for your lawn
Worked example
For a 12 m × 9 m back lawn with a 2 m round bed, and an 8 m × 6 m L-shaped front lawn with a 3 m × 2 m corner cut out:
- Back lawn: 104.86 m² (108 m² less 3.14 m² of bed).
- Front lawn: 42 m².
- Total: 146.86 m² (1,581 ft²) across 2 zones.
Every robot mower is rated for a lawn area in square metres, so that's the first number you need. Split your lawn into simple shapes, add each separate lawn as its own zone, and take away beds, patios and ponds.
How it works
- Rectangle: length × width.
- Circle: π × (diameter ÷ 2)².
- Triangle: from its three sides (Heron's formula), so you only need a tape measure, not a right angle.
- L-shape: the whole rectangle, minus the corner that's cut out.
- Points: for an irregular lawn, walk the edge and note how far across and along each corner is from a fixed point. The calculator joins them up.
Measure in metres or feet: the result is always in m², with ft² alongside. The total carries over to the robot mower chooser on this device.
FAQs
Should I include the bits the mower can't reach?
No. Take away beds, patios and ponds, and leave out strips too narrow for a mower. Include grass paths that link lawns, because the mower will cross them.
My lawn is a curvy shape. How accurate is this?
Break it into a few rectangles and triangles and you'll usually be close enough to choose a mower. For an odd shape, the points method is the most accurate.
Read the guide: How to measure your lawn
More tools
- Boundary wire or wire-free? DeciderAnswer six questions about your garden and see which navigation suits it: boundary wire, RTK satellite, camera vision, LiDAR or a hybrid, with the reasons and the trade-offs.
- Lawn slope calculator (% and °)Turn a rise and a distance, or a phone spirit-level reading in degrees, into slope % and °, find your steepest section, and check it against a mower's rated maximum.
- Which robot mower fits my lawn?Tell us your lawn's size, zones, steepest slope, narrowest passage and surroundings. We'll show which navigation tech suits it and which UK models are rated to cover it, each with its specs checked date.