Quick answer
A 10,000 sq ft lawn with a 21-inch mower at average speed takes about half an hour.
How it works
Your mower covers its deck width (minus about 15% for overlap) times your speed every hour. A 21-inch walk-behind covers roughly 20,000 sq ft per hour; a zero-turn covers several times that.
Formula
Time = Lawn area ÷ (Deck width × 0.85 × Speed)
Assumptions & limitations
- Open, mostly flat lawn
- 15% overlap between passes
- No trimming or edging time included
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
Why does it take me longer than the estimate?
Turns, obstacles, slopes, and thick grass all slow you down — add 20–30% for a complicated yard.
Is a riding mower worth it?
A common rule of thumb: once your lawn passes about half an acre, a rider starts paying for itself in time saved.