Grass Seed Calculator
Estimate how much grass seed your lawn needs. Enter your lawn dimensions, grass type and project type to get pounds of seed, number of bags and total cost.
Estimate Grass Seed, Bags and Cost for Your Lawn
Grass Seed Formula
Where:
- \(A\) — lawn area in ft²
- \(L\), \(W\) — length and width of a rectangular lawn (converted to feet)
- \(d\) — diameter of a circular lawn (converted to feet)
- \(r\) — seeding rate in lb per 1,000 ft², which depends on the grass type and whether you are seeding a new lawn or overseeding
The lawn area is computed first, based on the shape you choose, and everything entered in meters is converted to feet (1 m = 3.28084 ft) so a single seeding rate per 1,000 ft² can be used. The seed weight is then scaled to your lawn size, converted to whole bags by rounding up, and multiplied by the price per bag.
Grass Seed – Calculation Example
Example: a new rectangular lawn 40 ft long and 30 ft wide, seeded with Kentucky bluegrass. Seed is sold in 5 lb bags at $30 per bag.
\[ A = 40 \times 30 = 1200\ \text{ft}^2 \]
For a new Kentucky bluegrass lawn the calculator uses the midpoint of the typical 2–3 lb/1,000 ft² range, so \(r = 2.5\):
\[ \text{Seed} = \frac{1200}{1000} \times 2.5 = 3\ \text{lb} \]
Bags: \(3 \div 5 = 0.6\), rounded up to 1 whole bag. Cost: \(1 \times 30 =\) $30.
Result: a 1,200 ft² (111.5 m²) lawn needs about 3 lb (1.36 kg) of seed — buy one 5 lb bag for roughly $30.
How to Use the Calculator
- Pick the Lawn shape: rectangle, circle, or enter a known Total area directly. Only the fields for that shape are shown.
- Enter your dimensions in the Length and Width fields (or Diameter, or Total area) and set the unit to ft or m.
- Select the Grass type. Choose Custom only if your seed bag specifies a rate that is not listed — then fill in the Custom seeding rate and the season of your grass.
- Choose the Project: a new lawn from bare soil or overseeding an existing lawn. Overseeding uses roughly half the seed of a new lawn.
- Enter the Bag size in lb or kg and, optionally, the Price per bag. Leave the price empty if you only need the seed quantity.
What the Results Mean
The Lawn area is shown in both ft² and m², so you can double-check it against your measurements. The Seeding rate used is the midpoint of the typical range for your grass type and project — a starting point, not a rule set in stone.
Grass seed needed is the total weight of seed to spread over the whole lawn once. Spreading it evenly matters as much as the quantity: too little leaves thin spots, while too much causes seedlings to compete with each other and die off, wasting money.
Bags to buy is always rounded up to whole bags, since stores do not sell fractions of a bag. Estimated cost covers seed only — it does not include soil preparation, starter fertilizer, mulch, or delivery.
The When to seed panel gives timing advice for cool-season grasses (Kentucky bluegrass, fescues, ryegrass — best in early fall) and warm-season grasses (Bermuda, zoysia — best in late spring to early summer). Timing has a bigger effect on success than almost any other factor, because seedlings need the right soil temperature to germinate and enough time to establish before weather stress.
Seeding Rates by Grass Type
| Grass type | New lawn (lb/1,000 ft²) | Overseeding (lb/1,000 ft²) | Season |
|---|---|---|---|
| Kentucky bluegrass | 2–3 | 1–1.5 | Cool |
| Tall fescue | 6–8 | 3–4 | Cool |
| Perennial ryegrass | 5–7 | 3–4 | Cool |
| Fine fescue | 4–5 | 2–3 | Cool |
| Bermudagrass (hulled) | 1–2 | 1 | Warm |
| Zoysiagrass | 1–2 | 1 | Warm |
Use the lower end of the range on well-prepared, irrigated soil, and the upper end for heavy-traffic areas, erosion-prone slopes, or thickening up a poor existing lawn.
Assumptions, Limitations and Tips
- The seed bag label wins. If the label on your product specifies a rate, use it — seed quality (germination and purity percentages) varies between brands, and coated seed needs higher rates by weight because part of the weight is coating, not seed.
- Buy a small buffer. Many people round up one extra bag for touch-ups a few weeks after germination, when bare patches appear. Because bags are rounded up automatically, the buffer often costs nothing.
- Good seed-soil contact is assumed. Rake the surface lightly before and after spreading, and keep the top inch of soil consistently moist until germination. If you are starting from scratch, prepare the ground first — the topsoil calculator helps you order the right amount of soil, and the square footage calculator can confirm odd-shaped areas.
- Seed or sod? Seeding is cheaper but takes weeks to establish. If you need an instant lawn, the sod calculator estimates rolls and cost for the same area.
- Estimates only. Actual needs vary with weather, watering, soil condition and how evenly your spreader distributes. Treat the result as a shopping estimate, not a guarantee.
Frequently Asked Questions
How do I calculate grass seed by hand without a calculator?
Measure your lawn and multiply length by width to get the area in ft²; for a circle, multiply the diameter by itself, then by 3.14, then divide by 4. Divide the area by 1,000 and multiply by the seeding rate for your grass type. For example, a 500 ft² patch of new tall fescue at about 7 lb/1,000 ft² needs \( 0.5 \times 7 = 3.5 \) lb of seed.
How much grass seed do I need for 1 acre?
One acre is 43,560 ft², or about 43.56 units of 1,000 ft². Multiply that by your seeding rate. For a new Kentucky bluegrass lawn at 2.5 lb/1,000 ft², that is roughly 109 lb of seed; tall fescue at 7 lb needs about 305 lb. For an acre or more, buying seed in 25 or 50 lb bulk bags is usually far cheaper per pound than small retail bags.
How do I convert seeding rates from lb per 1,000 ft² to kg per m²?
Divide the lb/1,000 ft² rate by 2.47 to get kg per 100 m², since 1,000 ft² equals 92.9 m². For kg per m², divide the rate by 2,205 — a rate of 5 lb/1,000 ft² is about 0.0023 kg/m². Seed sold in Europe is often labeled in g/m²; multiply g/m² by 20.43 to compare it with lb/1,000 ft².
Why does my lawn need less seed when I overseed than when I plant new?
A new lawn starts from bare soil, so the seed must produce every single plant with no room for error. Overseeding thickens grass that is already there, so existing plants fill part of the space — that is why the overseeding rate is roughly half the new-lawn rate. Spreading a full new-lawn rate over existing grass wastes seed and crowds seedlings, causing many of them to die off.
Does coated seed need a different amount than uncoated seed?
Yes. Coated seed is wrapped in materials that help it retain water, but the coating can add 30–50% to the total weight, so a pound of coated seed contains fewer actual seeds than a pound of raw seed. Check the label — coated seed often specifies a higher application rate. Germination and purity percentages on the label also tell you how much of the weight is live, usable seed.
How do I measure the area of an irregular or L-shaped lawn?
Break the lawn into rectangles and triangles, measure each part, and add the areas together. For an L-shape, split it into two rectangles and sum them. For curves, take several width measurements across the lawn, average them, and multiply by the length — close enough for buying seed. Then enter the result through the Total area option instead of trying to fit it into a single rectangle or circle.
Can I put down too much grass seed?
Yes, and it is a common and expensive mistake. Over-seeded lawns produce dense clumps of seedlings that compete for light, water and nutrients; many die off, and the survivors stay weak and prone to disease. Stick to the recommended rate, spread half the seed in one direction and the other half at a right angle for even coverage, and resist the urge to dump extra seed on thin spots all at once.