Measure it once. Use it often.

Lawn area

For one rectangle, subtract beds and paving inside it. Split an irregular lawn into smaller rectangles and add their results. This estimates area, not a fertilizer application rate.

Formula: length × width − excluded area.

Example: 40 ft × 25 ft − 100 sq ft of beds = 900 sq ft of lawn.

Sprinkler runtime from catch cups

Use four or more identical, straight-sided containers on a level surface across one sprinkler area. Enter every reading, including zero. Use the same depth unit throughout.

Formula: target depth ÷ average collected depth × test minutes.

Choose the additional water target from your grass, soil, recent rain, restrictions and local advice. This calculator does not set a universal weekly allowance. The output is a total runtime estimate; the test already applied water. Pause if runoff begins and reassess coverage before running longer.

Example: 0.2 inches collected in 15 minutes means a 0.3-inch additional target would take about 22.5 minutes at the same rate.