Grass Seed Calculator

Turn a lawn into pounds of seed, using the coverage per pound for the grass you are actually sowing.

The area

The lawn

In feet, measured on the ground. An awkward shape is easier as two or three rectangles added together than as one average.
In feet. Measure to where the grass actually stops, not to the fence, and leave out beds, paths and anything else you are not seeding.

What you are buying

Extension services publish this the other way up, as pounds per 1,000 square feet, so divide 1,000 by that rate. Kentucky gives tall fescue 6 lb, which is the 167 here; perennial ryegrass 4 to 6 lb, so 167 to 250; Kentucky bluegrass 2 lb, so 500; seeded bermudagrass 1 to 2 lb, so 500 to 1,000. Kansas State puts tall fescue at 6 to 8 lb for a new lawn and 3 to 5 to thicken a thin one, so roughly double this figure when you are overseeding rather than starting from bare soil.
The price of one pound. A bag states its weight, so divide the bag price by the pounds in it. Starter fertilizer, straw and topdressing are not counted here.
Ten percent covers the edges and the second pass most people end up making. Resist going higher: Kansas State warns that seeding too heavily weakens the stand, because the seedlings compete with each other rather than filling in. 10.00%
What to buy
7 pounds
9%
is spare
Surface to cover 1,000 sq ft
Waste allowance 100 sq ft
Material must cover 1,100 sq ft
Measured area
1,000 sq ft
After deductions
1,000 sq ft

The detail

Spare once finished 169 sq ft
Material cost $0

Every figure here is a planning estimate, not a professional takeoff. Yields, waste factors and code requirements vary by product, supplier and jurisdiction, so confirm quantities against the manufacturer’s data and your local building department before you order.

Generated by Mathterial

Every seeding rate you will ever read is published the same way, as pounds per 1,000 square feet, and every bag is priced by weight. So the whole job is turning your lawn into that one ratio and buying against it. This grass seed calculator does that from the lawn dimensions, and the number it needs from you is how much ground one pound covers.

Coverage per pound, by grass

The University of Kentucky Cooperative Extension Service publishes seeding rates by species in AGR-52. Divide 1,000 by the rate and you have the figure this calculator asks for.

GrassRate per 1,000 sq ftCoverage per pound
Kentucky bluegrass2 lb500 sq ft
Tall fescue6 lb167 sq ft
Perennial ryegrass4 to 6 lb167 to 250 sq ft
Bermudagrass, seeded1 to 2 lb500 to 1,000 sq ft

Tall fescue at 167 square feet to the pound is the default above, because it is the most widely planted of the four and the heaviest feeder of the set. Zoysiagrass is missing on purpose: Kentucky describes seeding it as erratic and slow, and it is normally planted as plugs or sprigs instead.

Overseeding takes about half

Spreading seed into a lawn that already exists is a different job from starting on bare soil, and the rate halves. K-State Research and Extension gives tall fescue 6 to 8 pounds per 1,000 square feet for a new lawn, the same 6 to 8 for overseeding large dead patches, and 3 to 5 for overseeding to thicken a lawn that is merely thin.

In the field above that means roughly doubling the coverage figure when you are thickening rather than establishing. Tall fescue goes from 167 square feet per pound to something nearer 250 or 330.

More seed is not a better lawn

This is the one place where rounding generously works against you. K-State warns that seeding either too lightly or too heavily weakens the stand. Sown thick, the seedlings compete with each other for the same water and light instead of filling in, and you get a dense flush that thins out badly in its first summer.

The waste allowance here is set at 10 percent, which covers the edges and the overlapping second pass almost everyone makes. It is not a reason to buy half again as much.

A pound of bag is not a pound of seed

Published rates for several species are given in pure live seed, which is the share of the bag that is both the grass you wanted and able to germinate. Kentucky’s AGR-50 gives the arithmetic: purity multiplied by germination, divided by 100.

Its worked example uses a tag reading 49 percent purity and 85 percent germination. That is 41.65 percent pure live seed, so a rate of 1 pound per 1,000 square feet needs 2.4 pounds of that actual bag to deliver it. A bag can be more than half filler and inert matter and still be sold honestly, because the tag says so.

So read the tag before you trust the weight. If purity and germination are both high, the published rate and the bag weight are close enough to treat as the same thing. If they are not, divide the coverage figure above by the pure live seed percentage before entering it.

When to put it down

Rate and timing are not independent, and timing is the one you cannot buy your way out of. For cool season grasses Kentucky gives mid-August to late September as the best window, with mid-February to mid-March as the fallback and nothing later than mid-April. Seed sown outside those windows germinates into competition from crabgrass or into a summer it is not rooted enough to survive.