Lawn Size Calculator
Measure lawn area in square feet, square meters and acres from rectangles, circles and triangles, and estimate fertilizer and seed amounts.
Updated Formula covered by automated tests
Every bag of lawn fertilizer, grass seed or weed control is labeled with how many square feet it covers, so the first job before a trip to the garden center is knowing how big your lawn actually is. This tool measures the turf in square feet, square meters and acres from a few tape-measure readings, then estimates how much fertilizer product and seed that area takes.
Few yards are a perfect rectangle. Measure the lawn as a set of rectangles, circles and triangles, run each shape through the calculator, and add the areas. Leave out the house, driveway, patio and planting beds, because spreading product on them wastes money and washes nitrogen into storm drains.
The formula
- A
- Lawn area in square feet
- L, W, r, b, h
- Length, width, radius, triangle base and triangle height, all in feet
- N rate
- Pounds of actual nitrogen per 1,000 sq ft per feeding; this tool uses 1 lb, a common upper figure for a single application
- N%
- Nitrogen percentage, the first number of the N-P-K grade printed on the bag (24 for a 24-0-6 product)
- seed rate
- Pounds of seed per 1,000 sq ft for a new lawn, which depends on the grass species
The area formulas are ordinary geometry. The metric factor is exact: an international foot is defined as 0.3048 m, so a square foot is 0.3048² = 0.09290304 m². An acre is 43,560 sq ft, historically one chain (66 ft) by one furlong (660 ft).
Lawn feeding recommendations from university extension services are written in pounds of nitrogen per 1,000 square feet, not pounds of product. A bag labeled 24-0-6 is 24 percent nitrogen by weight, so delivering 1 lb of nitrogen takes 1 ÷ 0.24 = 4.17 lb of that product. The higher the first number, the less product you spread.
Worked example
Priya’s back lawn is a 60 by 45 ft rectangle plus a triangular corner with a 30 ft base and 20 ft depth. She has a 24-0-6 fertilizer and plans to reseed bare patches at 4 lb per 1,000 sq ft if she ever redoes the whole lawn.
- 1 Rectangle: 60 × 45 = 2,700 sq ft.
- 2 Triangle: ½ × 30 × 20 = 300 sq ft.
- 3 Total lawn: 2,700 + 300 = 3,000 sq ft, which is 3,000 × 0.09290304 = 278.71 m² or 3,000 ÷ 43,560 = 0.0689 acres.
- 4 Nitrogen for one feeding: 3,000 ÷ 1,000 × 1 = 3 lb of N.
- 5 Fertilizer product: 3 ÷ 0.24 = 12.5 lb of the 24-0-6 bag.
- 6 Seed for a full renovation: 3,000 ÷ 1,000 × 4 = 12 lb.
Result: Priya has 3,000 sq ft of lawn. One feeding takes 12.5 lb of her 24-0-6 fertilizer, and reseeding the whole lawn would take 12 lb of seed.
Before you rely on the result
- Results are only as good as your measurements; pacing a lawn instead of using a tape can be off by 10 percent or more.
- The nitrogen rate is a generic figure. Grass species, season, soil test results and local rules (some states limit phosphorus and nitrogen near water) should decide how much and how often you feed.
- Always follow the product label, which is the legal guide for application rates of fertilizers and pesticides.
Frequently asked questions
How do I measure a curved or kidney-shaped lawn?
Draw a long straight line through the middle, then measure the width at equal intervals along it, say every 10 ft. Multiply the average of those widths by the length of the line. For a curved edge you can also fit the largest rectangle inside and add semicircles or triangles for the bulges.
Why does the fertilizer amount change when I change the N-P-K number?
The tool targets a fixed amount of nitrogen, the nutrient grass uses most. A 10-10-10 garden fertilizer is only 10 percent nitrogen, so you need 10 lb of it per 1,000 sq ft, while a 32 percent lawn product needs just over 3 lb. Spreader settings on the bag are already worked out this way.
How much grass seed do different grasses need?
Seed size varies enormously. Fine-seeded Kentucky bluegrass is often sown at around 2 to 3 lb per 1,000 sq ft, while larger-seeded tall fescue is often sown at 6 to 8 lb. Overseeding a thin lawn usually takes about half the new-lawn rate. Use the rate on your seed bag in the seed rate box.
Should I measure slopes along the ground or flat?
For product coverage, measure along the ground surface, because that is the area the granules land on. On gentle slopes the difference is tiny; on a steep bank it can add 10 percent or more.
Sources
- NIST Special Publication 811: Guide for the Use of the SI (nist.gov)
- Penn State Extension (lawn and turf guidance) (extension.psu.edu)