Grass Seed Calculator

How to use the grass seed calculator

Measure the lawn in feet, length times width, and split odd shapes into two or three rough rectangles rather than trying to be clever about curves — run the calculator once per section and add the pounds. Seed quantity is forgiving at the edges in a way that paint and tile are not, because a broadcast spreader throws a wide, feathered pattern anyway and you will be walking overlapping passes.

Pacing off an established yard is genuinely accurate enough. What is not forgiving is the rate, which is why the species select does the real work on this page. Get the area wrong by ten percent and nothing bad happens; get the species wrong and you can be out by a factor of six.

Rates differ this sharply because they are really seedling counts wearing weight units. A lawn needs a target number of seedlings per square inch, and grass seed varies enormously in size between species, so the small-seeded grasses deliver that count in far fewer pounds. Published extension figures show the spread clearly.

The project select halves the rate for overseeding, which is spreading seed into a lawn that already exists to thicken it. That halving is not a rounding convenience — existing turf already occupies most of the soil contact a seedling needs, so seed applied at a full new-lawn rate largely feeds birds and washes into the gutter.

MSU Extension reflects the same gap from the other direction, quoting 6 to 8 lb per 1,000 sq ft of tall fescue for a complete renovation against overseeding rates of 1.5 to 2 lb for Kentucky bluegrass and 3 to 5 for ryegrass and fine fescue mixes. Use the new-lawn setting only for genuinely bare ground: a fresh grade, a renovation after killing off the old turf, or patches raked back to soil.

Does the timing matter more than the rate?

Spend the effort on timing instead, because timing is what actually decides the outcome. UGA Extension puts tall fescue seeding in September to October or late February through March, and says warm-season grasses go in once soil at the 4-inch depth is consistently 65 degrees Fahrenheit and rising, which is typically mid to late spring.

Seed a cool-season lawn in June or bermudagrass in October and no rate will rescue it; seed in the right window and these numbers produce a full stand in one season.

The formula, worked line by line

Everything about seed quantity is quoted per 1,000 square feet, which is the unit the extension services, the bag labels and the spreader settings all agree on. So the arithmetic is only two steps: convert your lawn into thousands of square feet, then multiply by the rate for the species you are sowing. Divide the area by 1,000 first and the rest is a single multiplication you can do in the store aisle.

The third term is the project factor, and it exists because bare soil and established turf are different jobs. New seeding assumes every seed has a shot at soil contact. Overseeding assumes most of the ground is already occupied by grass, so only a fraction of what you spread can reach dirt at all — hence the 0.5.

Doubling the rate does not double the number of seedlings that establish; it mostly doubles the number that never make it out of the thatch.

lbs of seed = (length × width ÷ 1,000) × rate × project factor
rates (new lawn, lbs/1,000 sq ft): tall fescue 7 · rye 8 · fine fescue 5 · KBG 3 · bermuda 1.5
project factor: new lawn = 1 · overseeding = 0.5

Be honest with yourself about which rate you are using, because this tool leans generous. Penn State Extension publishes 6 to 8 lb per 1,000 sq ft for turf-type tall fescue and 4 to 5 for a pure stand of turf-type perennial ryegrass; UGA Extension publishes 5 to 6 for tall fescue in Georgia. The presets here are 9 and 8.

That extra margin buys forgiveness on rough seedbeds and poor irrigation, and it costs you seed and, at the extreme, stand quality. If the bag in your hand prints a rate, that rate reflects the actual cultivar and its actual seed count, and it should win.

Two label numbers decide whether the pounds you buy are the pounds you sow. MSU Extension advises never buying seed under 70 percent germination, keeping inert matter under 4 percent and weed seed under 1 percent, and buying only seed tested within the previous 12 months.

A bag at 85 percent germination and 95 percent purity delivers about 81 percent pure live seed, so 10 lb of it puts roughly 8 lb of viable seed on the ground; a bargain bag heavy on inert filler is not the bargain it looks like. Finally, this is a quantity estimate, not an agronomy plan — soil test results, drainage and shade are what decide whether the stand actually holds.

Questions people ask