Grass Seed Calculator

Grass seed calculator that turns lawn area, grass type and project into pounds and bags of seed, shows rates per 1,000 sq ft, acre and m², and checks the live seed on the seed tag.

How a Grass Seed Calculator Finds the Pounds You Need

Grass seed rates are given in pounds per 1,000 square feet, so every estimate starts with the lawn area. A grass seed calculator divides that area by 1,000 and multiplies by the seeding rate for your grass type and job.

$$S=\frac{A}{1000}\times R\times G\times C\times P$$

S is seed in pounds, A is the lawn area in square feet and R is the new-lawn rate in lb per 1,000 sq ft. G is 1 for a new lawn or patch and 0.5 for overseeding, C is 1.5 for a poor site and P raises the rate when the seed tag shows low live seed.

In the grass seed calculator, a 5,000 sq ft tall fescue lawn at 8 lb per 1,000 sq ft needs 40 lb of seed for a new lawn. Overseeding the same lawn takes 20 lb, and a dry slope or late sowing pushes the new-lawn figure to 60 lb.

Recommended Seeding Rate for Grass by Species

Seeding rates vary more than tenfold between grasses, because seed size varies just as much. A pound of Kentucky bluegrass holds about 2,177,000 seeds, while a pound of tall fescue holds about 227,000, so bluegrass covers far more ground per pound.

The cool-season ranges come from the UMass Extension seeding rate fact sheet. The bermudagrass, zoysia and centipedegrass ranges and all germination times come from University of Tennessee Extension W160-B, which says to double the rate for unhulled bermudagrass seed. Buffalograss follows a University of Arizona bulletin, and bahiagrass follows UF/IFAS.

St. Augustinegrass is missing on purpose. UF/IFAS gives no seeding rate for it, because it is planted from sod or plugs, so the grass seed calculator points you to sod instead of a seed amount.

Store charts often show 10 lb per 1,000 sq ft for tall fescue and ryegrass, above the 7 to 9 lb UMass range, while UT Extension lists a lower 5 to 8 lb for tall fescue and 4 to 6 lb for ryegrass. The grass seed calculator uses the middle of the extension range by default, and the low or high end can be picked when the site calls for it.

How Much Grass Seed Do I Need for My Lawn?

For a new tall fescue lawn, you need about 8 lb of seed per 1,000 sq ft, or 40 lb for a 5,000 sq ft yard. The chart shows the same seed at common lawn sizes, with 25 lb bags rounded up for a new lawn.

The grass seed calculator handles rectangles, circles, ovals and triangles. For an odd-shaped yard, split it into simple shapes and add the areas. An 80 × 60 ft rectangle is 4,800 sq ft, a 70 ft circle is 3,848 sq ft and a triangle with an 80 ft base and 60 ft height is 2,400 sq ft.

Take out beds, patios and the house footprint before buying. Removing 800 sq ft of beds from the 80 × 60 ft rectangle drops a new tall fescue order from 38.4 lb to 32 lb.

Grass Seed Calculator per Acre

One acre is 43,560 sq ft, so the per-acre rate is the per-1,000 sq ft rate times 43.56. A new tall fescue or perennial ryegrass acre needs about 348 lb, which is 14 bags of 25 lb or 7 bags of 50 lb.

Small-seeded grasses need far less. An acre of Kentucky bluegrass takes about 65 lb, and hulled bermudagrass takes about 33 lb, so a single 50 lb bag of hulled bermuda covers more than an acre at the middle rate.

For overseeding an acre, the grass seed calculator halves the new-lawn figure. For tall fescue that is 174 lb, or seven 25 lb bags.

How Much Does a Bag of Grass Seed Cover?

A bag covers its weight divided by the seeding rate, times 1,000. At the tall fescue new-lawn rate of 8 lb per 1,000 sq ft, a 50 lb bag covers 6,250 sq ft, and the same bag overseeds 12,500 sq ft.

These figures are for tall fescue. The grass seed calculator reworks every row for the grass you pick, so a 25 lb bag of Kentucky bluegrass at 1.5 lb per 1,000 sq ft covers 16,667 sq ft of new lawn.

If you already have seed, run the grass seed calculator from the weight instead of the area. A 15 lb bag of tall fescue seeds 1,875 sq ft of new lawn or overseeds 3,750 sq ft.

Grass Seed per Square Meter for Metric Lawns

Metric rates are given in grams per square meter, and the grass seed calculator reports both units. Tall fescue at 8 lb per 1,000 sq ft equals 39.1 g/m², so 100 m² takes about 3.9 kg of seed for a new lawn and about 2 kg for overseeding.

One kilogram of tall fescue seeds about 25.6 m², and a 5 kg bag seeds 128 m². A 20 kg bag covers 512 m² new or about 1,024 m² overseeded.

Seeds per square meter depend on the grass. At those rates, tall fescue drops about 19,547 seeds per m² and Kentucky bluegrass about 35,150, because its seeds are so much smaller. In square feet, that is about 1,816 and 3,266 seeds.

Grass Seed Calculator for Overseeding

Overseeding a thin lawn takes about half the new-lawn rate, the usual retail rule, since the existing grass still covers part of the soil. A 5,000 sq ft tall fescue lawn needs 20 lb for overseeding against 40 lb for bare soil.

Bare patches are different from a thin lawn. Patch repair uses the full new-lawn rate on the patch area only, because the soil there is bare.

A lawn needs more seed when soil shows between the grass plants, when thin areas stay thin after feeding and watering, or after drought, grubs or heavy traffic. Seeding into those gaps before weeds fill them is what overseeding is for.

Overseeding Bermuda With Ryegrass in Winter

Bermudagrass turns brown when it goes dormant, so many Southern lawns are overseeded with ryegrass for winter color. The grass seed calculator uses one fixed rate for this of 5 lb per 1,000 sq ft, from Clemson Extension, rather than a new-lawn and overseeding pair.

A 5,000 sq ft bermuda lawn takes 25 lb, exactly one 25 lb bag, and an acre takes about 218 lb. Clemson advises sowing about 30 days before the first frost and overseeding bermudagrass only, because ryegrass can damage centipede, zoysia and St. Augustine lawns.

Grass Seed Blends and Clover

Most bags hold a blend, such as tall fescue with a little Kentucky bluegrass. A blend's rate is the share-weighted average of each grass's rate, with shares taken by weight from the seed tag and adding up to 100%.

$$R_{blend}=\sum p_i\times R_i$$

p_i is each grass's share by weight and R_i is its own rate. An 85% tall fescue and 15% Kentucky bluegrass blend works out to 0.85 × 8 + 0.15 × 1.5 = 7.03 lb per 1,000 sq ft, or 35.1 lb for a 5,000 sq ft new lawn.

That blend averages about 519,500 seeds per pound, so it spreads roughly 3,650 seeds per sq ft. The small bluegrass seed makes up most of the count even at 15% of the weight.

Microclover goes into an existing lawn at 1 lb per 1,000 sq ft, according to DLF, so the grass seed calculator gives 5 lb of clover seed for 5,000 sq ft. For a new lawn, DLF suggests mixing Microclover in at 5% of the grass seed weight instead.

Seed Tags, Poor Sites and Too Much Seed

The seed tag lists purity and germination, and multiplying them gives the pure live seed share. UMass lists minimum pure live seed of 80.75% for tall fescue, 67.5% for Kentucky bluegrass, 85.5% for perennial ryegrass and 76% for red fescue.

$$P=\frac{PL{S}_{min}}{purity\times germination}$$

P only applies when the tag falls short of the minimum. A tall fescue tag with 85% purity and 80% germination gives 68% live seed, so the grass seed calculator raises the rate 18.8%, from 8 to 9.5 lb per 1,000 sq ft.

UMass also advises raising seeding rates about 50% to make up for poor conditions, such as a dry slope, no irrigation or late sowing. Applied in the grass seed calculator, that takes tall fescue from 8 to 12 lb per 1,000 sq ft, or 60 lb for a 5,000 sq ft lawn.

You can put down too much grass seed. Crowded seedlings compete for water, light and nutrients, which leaves a thin, weak stand, so a seed rate above the high end of the range rarely helps.

Grass Seed Cost and the Best Time to Plant

Seed cost is the pounds ordered times the price per pound. At a sample $3.50 per lb, a new tall fescue lawn costs $28 per 1,000 sq ft, and two 25 lb bags for a 5,000 sq ft yard come to $175.

Cool-season grasses germinate well with air temperatures cycling between about 59 and 82°F, and warm-season grasses at about 68 to 95°F, according to UT Extension W160-B. That points cool-season seeding to late summer and early fall, and warm-season seeding to late spring and early summer.

Seed is the low-cost way to start a lawn but takes weeks to fill in. For a lawn you need right away, the Sod Calculator works out rolls and pallets for the same area.