What size robot mower do I need for my lawn?

Start by measuring the lawn area, then choose a mower whose rated area is comfortably bigger, around 20% or more above your lawn, rather than one that only just covers it.

The rated area, given in square metres, is the maximum lawn the manufacturer says the mower can keep on top of. It usually assumes ideal conditions: a simple shape, flat ground and the mower running for long hours through the week. Real gardens cut that down. Things that eat into capacity include:

• Several separate zones or a narrow passage the mower has to travel through
• Slopes, which drain the battery faster
• Lots of trees, beds and obstacles to work around
• A daylight-only schedule, which we recommend for wildlife

Buying a size up means the mower can finish in fewer, shorter sessions, which leaves room to avoid evenings and wet days. Buying too small leads to a lawn that never looks quite finished.

To measure, pace out the lawn or trace it on an online map. Our lawn size tool lets you draw the outline on a satellite view and gives the area. Then use the mower finder to shortlist models by area, slope and budget. Rough guide: a typical small terraced-house lawn is under 200 m², a larger suburban garden is often 300 to 800 m², and 1,000 m² or more is a big lawn by UK standards.