Formula
Rectangle area = length × width. Circle area = π × (diameter ÷ 2)². Total = rectangle + circle; square yards = square feet ÷ 9. Example: a 40 ft × 25 ft lawn is 1,000 sq ft, or 111 sq yd.
How to use it, step by step
Measure the main rectangular part of the lawn in feet, excluding paths, beds and driveways. If part of the lawn is circular — around a tree or a round bed — measure its diameter and enter it; otherwise leave it at 0. The calculator gives total area in square feet and square yards, because seed and fertilizer labels use both units. For an irregular lawn, split it into rectangles and circles, calculate each, and add them.
Worked example in detail
A lawn 40 ft × 25 ft is 1,000 sq ft. Add a circular section 10 ft across: π × 5² = 78.5 sq ft, total 1,078.5 sq ft, or about 120 sq yd. That total is what you enter in the lawn seed calculator (area) and the fertilizer calculator (area), so measuring the lawn once serves both jobs.
What affects real lawn area
Slopes make a lawn larger than its footprint on a map, but for seed and fertilizer the flat area is the right figure — you buy seed for the ground you can see, not the slope's extra surface. Exclude areas you do not want to seed or feed, such as a wildflower strip or a paved area inside the lawn, or you will over-order. Re-measure after any landscaping change rather than reusing last year's area.
Frequently asked questions
Why square yards as well as square feet?
Seed, fertilizer and turf are often sold per square yard or per 1,000 square feet. Having both numbers means you do not have to convert at the shop.
What if my lawn is not a rectangle or circle?
Split it into rectangles, triangles and circles, calculate each part, and add them. A rough split that is close is better than guessing the whole area at once.
Should I include the area under trees?
Only if you seed and feed it like lawn. Under dense shade, grass grows poorly anyway — consider mulch or ground cover there instead of lawn seed.