Lawn Area Calculator
Measure your lawn by shape, in feet or meters, and get the seed shopping list in the same run: area in square feet, square yards and acres, the pounds of seed for your exact grass type, the whole bags to buy, and the cost. Rectangle, square, circle and triangle lawns are all covered, for a new lawn or for overseeding.
Seeding rates are standard agronomic rates in lbs per 1,000 sq ft; always check the rate on your seed bag.
Quick Answer
A 40 × 30 ft rectangle is 1,200.0 sq ft (133.33 sq yd). As a new Kentucky bluegrass lawn at 3.0 lbs per 1,000 sq ft, it needs 3.6 lbs of seed: 1 bag of the 10 lb size, $45.00 at $45 a bag. The calculator above is pre-filled with this lawn.
Key takeaways
- The grass type moves the answer more than the measurements do: rates run from 0.5 lbs per 1,000 sq ft (centipede) to 8.0 lbs (tall fescue).
- Overseeding uses roughly half the new-lawn rate for every grass in the picker.
- Bags always round up: 3.6 lbs needed with 10 lb bags still means buying 1 bag.
- Always check the rate on your seed bag: it overrides any general table, this one included.
- Quick Answer
- How to use the lawn area calculator
- The formulas behind the area and seed numbers
- Worked example: a 40 by 30 ft backyard, checked against the tool
- Standard seeding rates, and why the grass matters more than the tape measure
- Measuring odd-shaped lawns without guessing
- Seed or sod: the honest cost picture
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
How to use the lawn area calculator
Pick the shape, enter the measurements, then choose your grass and project type: the tool sets the rate, works out the pounds, rounds up to whole bags and prices it. Results stay hidden until you click Calculate.
- Shape and unit: rectangle, square, circle or triangle, in feet or meters. The second measurement field hides itself for squares and circles.
- Dimensions: for a circle, enter the radius, half the diameter. A 40 ft wide round lawn has a radius of 20 ft, not 40.
- Grass type: this sets the rate in lbs per 1,000 sq ft. Extension services put tall fescue at 6 to 8 lbs and Kentucky bluegrass at 2 to 3 lbs for new lawns, per the University of Nebraska-Lincoln fall seeding guidance; the picker uses the top of each range.
- Project type and density: new lawn takes the full rate, overseeding takes half, and the density multiplier (0.8x, 1.0x or 1.2x) adjusts for a light touch-up or a thicker stand.
- Bag size and price: pick the bag you will actually buy, and add its price if you want the cost line.
Once the new lawn is established, the recurring question becomes what it costs to keep it cut: the lawn mowing cost calculator prices a visit from this same area figure, by the square foot, by the hour, or as a flat rate.
The formulas behind the area and seed numbers
Area comes from the standard geometry formula for your shape, and seed is that area scaled by the seeding rate for your grass. Every output line shows its own working in the result box.
Square area = Side × Side
Circle area = π × Radius²
Triangle area = (Base × Height) ÷ 2
Seed (lbs) = (Area in sq ft ÷ 1,000) × Seeding rate × Density
Bags = Seed ÷ Bag size, rounded up | Cost = Bags × Price per bag
Three conversions sit underneath: square yards are square feet divided by 9, acres are square feet divided by 43,560 (printed once the lawn reaches 0.05 acres), and meters convert to feet first at 1 metre = 3.28084 feet. Kansas State University’s fall turfgrass seeding recommendations use the same rate structure, with about half the new-lawn rate when seeding into an existing lawn.
Worked example: a 40 by 30 ft backyard, checked against the tool
The pre-filled run is a 40 × 30 ft rectangle, Kentucky bluegrass, new lawn, standard density, 10 lb bags at $45. Here is every line the calculator returns, plus the variations readers ask about most.
| Run | Area (sq ft) | Seed (lbs) | Bags (10 lb) | Cost |
|---|---|---|---|---|
| Worked example: 40 × 30 ft, Kentucky bluegrass, new | 1,200.0 | 3.6 | 1 | $45.00 |
| Same lawn, overseeding instead | 1,200.0 | 1.8 | 1 | $45.00 |
| Same lawn, tall fescue, new lawn (rate 8.0) | 1,200.0 | 9.6 | 1 | $45.00 |
| Circle, radius 20 ft, Kentucky bluegrass, new | 1,256.6 | 3.8 | 1 | $45.00 |
| Rectangle 10 × 5 m, Kentucky bluegrass, new | 538.2 | 1.6 | 1 | $45.00 |
| Near an acre: 200 × 218 ft, tall fescue, overseeding | 43,600.0 | 174.4 | 18 | no price set |
Two things stand out. First, the bag count barely moves on a small lawn: anything up to 10 lbs of seed is one bag, so the rate matters more than the price per bag. Second, the meter row is a true conversion: 10 × 5 m is 50 sq m, and 50 × 10.764 = 538.2 sq ft. If you know a parcel size in acres instead, the acreage calculator converts between acres, square feet and square meters.
Standard seeding rates, and why the grass matters more than the tape measure
A 10 percent measuring error changes your seed order by 10 percent. Picking the wrong grass rate can change it by 300 percent or more, because seed size varies enormously by species: a pound of Kentucky bluegrass holds well over a million seeds, while a pound of tall fescue holds a fraction of that. The rates below are the exact presets in the picker.
| Grass type | New lawn (lbs / 1,000 sq ft) | Overseeding (lbs / 1,000 sq ft) |
|---|---|---|
| Centipede grass | 0.5 | 0.25 |
| Bermuda grass | 2.0 | 1.0 |
| Zoysia grass | 2.0 | 1.0 |
| Kentucky bluegrass | 3.0 | 1.5 |
| Buffalo grass | 3.0 | 1.5 |
| Fine fescue | 4.0 | 2.0 |
| Perennial ryegrass | 6.0 | 3.0 |
| Sun and shade mix | 6.0 | 3.0 |
| Tall fescue | 8.0 | 4.0 |
What that means on a mid-size 5,000 sq ft lawn, new seeding:
The presets sit inside the published extension ranges. Cornell University’s sports field program lists Kentucky bluegrass at 1 to 3 lbs per 1,000 sq ft and tall fescue at 6 to 8 lbs in its seeding rates guidance; the University of Georgia’s establishment bulletin gives bermudagrass at 1 to 2 lbs (hulled), centipedegrass at 0.25 to 1 lb, and zoysiagrass at 1 to 3 lbs. One honest gap: St. Augustine is missing from the picker because it is planted from sod or plugs, not seed.
Measuring odd-shaped lawns without guessing
Split the lawn into rectangles, squares, circles and triangles, run each piece through the tool, and add the areas. Curved beds and freeform edges are the only real source of error.
Worked through once: an L-shaped yard of a 30 × 20 ft rectangle (600 sq ft) plus a 15 × 10 ft rectangle (150 sq ft) is 750 sq ft. At the Kentucky bluegrass new-lawn rate that is (750 ÷ 1,000) × 3.0 = 2.3 lbs of seed. Subtract the house, driveways and beds from a whole-lot figure: seed only goes on grass. Levelling with topsoil comes first for most beds, and the landscape volume calculator works out material volumes by area and depth. For overseeding, Cornell’s overseeding guidance stresses the skipped step: seed has to reach soil, so mow short, rake or aerate, and keep the surface damp until germination.
Seed or sod: the honest cost picture
Seed wins on material cost and loses on time: a seeded lawn takes weeks to become usable, while sod is a lawn the day it goes down.
On the worked example, seeding 1,200 sq ft costs one $45 bag. Sodding the same area costs several times more before anyone is paid to lay it; the sod cost per square foot calculator prices that side by area and rate. Seed also offers far more varieties than sod. Sod earns its premium on slopes, where seed washes away, and when the lawn must look finished for a specific date. Timing matters too: the University of Missouri Extension’s cool-season grass guidance notes that an early-fall seeding establishes at the standard rate, while a late spring seeding often needs the dense setting.
What competing calculators miss
Most grass seed calculators do one half of this job well and skip the other half:
- DIYMeter’s seed and turf calculator: a tidy shopping list with bags and cost, but its seed formula is one flat rate (area ÷ 1,000 × 4 lbs) for every grass: double what bermuda needs, half what tall fescue needs. Rectangle-only, too.
- CalculatorLabs and CalcLoft: both ask you to type in your own seeding rate, the one number most homeowners do not know. A calculator that needs the answer as an input has skipped the hard part.
- HomeGPT’s lawn calculator: covers seed, sod and fertilizer in one tool, but only accepts length × width. Circular and L-shaped yards have no way in.
- SimpleMoney’s overseeding calculator: honest about the half rate, but overseeding only: no new lawns, no shapes, no bags, no cost.
- CalculatorsHub: prints the right formulas, then publishes an overseeding example that turns 5,000 sq ft at 4 lbs per 1,000 into 20 lbs without showing the scaling step clearly. Every number on this page is generated by the tool itself and re-verified against it.
- The gap this page fills: shape-based area (four shapes, feet or meters) feeding a per-grass rate engine with a new/overseed toggle, density factor, whole-bag rounding and a cost line, formula printed next to every result.
Frequently asked questions
Multiply length by width for a rectangle, side by side for a square, π × radius² for a circle, or (base × height) ÷ 2 for a triangle. The tool returns square feet, square yards and, for larger lawns, acres.
Use seed (lbs) = (area ÷ 1,000) × rate × density. A 1,200 sq ft new Kentucky bluegrass lawn needs (1,200 ÷ 1,000) × 3.0 × 1.0 = 3.6 lbs.
It depends on the grass: tall fescue 8 lbs, perennial ryegrass 6 lbs, fine fescue 4 lbs, Kentucky bluegrass 3 lbs, bermuda and zoysia 2 lbs, centipede just 0.5 lbs for a new lawn. Overseeding needs about half of each figure.
Divide the pounds needed by the bag size and round up: 9.6 lbs with 10 lb bags means 1 bag, with a little left over for patching. The tool does this for bag sizes from 3 lb to 50 lb.
Overseed when the lawn is thin but alive: it uses about half the seed, because the existing turf fills most of the ground. Start new when the lawn is mostly dead or you are changing grass types.
Yes. Choose the circle shape and enter the radius, half the diameter: a lawn 40 ft across has a radius of 20 ft and an area of about 1,257 sq ft. Entering the diameter instead quadruples the area, the most common round-lawn mistake.
Yes. Switch the unit to meters and enter your measurements as measured: the tool converts each dimension to feet (1 metre = 3.28084 feet) before working out the area, so a 10 × 5 m lawn correctly returns 538.2 sq ft, and the seed, bag and cost math runs on that converted area.
Split it into rectangles, triangles or circles, measure each piece, run each through the tool and add the areas. Add about 10% extra seed for curved edges, where straight-edged shapes slightly understate the true area.
On a very small area the exact need can be a few hundredths of a pound, which displays as 0.0 lbs at one decimal place. Any positive amount still rounds up to one whole bag, because a store will not sell you a spoonful.
Cool-season grasses (bluegrass, fescues, ryegrass) do best in early fall, with early spring second. Warm-season grasses (bermuda, zoysia, centipede, buffalo) go in late spring to early summer, once the soil is warm.
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References
- University of Nebraska-Lincoln Extension. Time for Fall Lawn Seeding. Accessed October 22, 2026.
- Kansas State University, Turfgrass Extension. Fall Turfgrass Recommendations and Tips. Accessed October 22, 2026.
- Cornell University, Safe Sports Fields. Seeding Rates for Sports Fields. Accessed October 22, 2026.
- University of Georgia Extension. Lawns in Georgia: Establishment (Bulletin 1533). Accessed October 22, 2026.
- University of Missouri Extension. Cool-Season Grass Cultivars and Seeding Rates (G6772). Accessed October 22, 2026.
- Cornell University, Safe Sports Fields. Routine Care: Overseeding. Accessed October 22, 2026.