Grass Seed Calculator
Find out exactly how much grass seed your lawn needs, or how far the seed you already have will stretch, using published seeding rates for 12 common species.
🌱 What is a Grass Seed Calculator?
A grass seed calculator turns a lawn measurement into a seed order. It multiplies the area you are seeding by a published seeding rate for the species you have chosen, then reports the weight of seed to buy and how many bags that comes to. The seeding rate is the part most people get wrong, because it is not a single number: it is specific to the grass species and to whether you are starting from bare soil or dropping seed into an existing lawn.
Rates vary far more than most gardeners expect, and the reason is seed size. A pound of Kentucky bluegrass holds roughly two million seeds, so 2 pounds spread over 1,000 square feet already lands a dense carpet of seedlings. A pound of perennial ryegrass holds only about 230,000 seeds, so the same coverage takes 7 pounds. Tall fescue, with even larger seed, wants 8. Warm season species sown from seed sit at the other extreme: bermudagrass goes down at about 1.5 pounds and centipedegrass at half a pound per 1,000 square feet. Using a bluegrass rate for fescue leaves bare ground, and using a fescue rate for bluegrass wastes three quarters of the bag.
Two further misconceptions cost people money. The first is that heavier seeding produces a thicker lawn. It does not: crowded seedlings compete for light and water, thin out at the first heat stress and are much more vulnerable to damping off, so an overseeded stand at double rate typically ends up worse than one seeded to label. The second is that bag weight equals usable seed. Purity and germination percentages on the tag multiply together into pure live seed, and a bag at 85 percent purity and 90 percent germination delivers only 76.5 percent of its weight as viable seed.
This calculator runs in both directions. Seed mode takes the lawn dimensions in feet or metres, applies the rate for your species and job, and returns pounds, kilograms, lawn area and the number of bags at your chosen bag size. Coverage mode does the reverse, taking the weight of seed you already have and telling you how much ground it will actually cover, with a chart showing how quickly that coverage collapses as the rate rises. Both modes list all twelve species side by side so you can see instantly what switching grass would cost.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — New Tall Fescue Back Lawn
60 ft × 40 ft of bare soil, tall fescue at 8 lb per 1,000 sq ft, 25 lb bags
Example 2 — Overseeding a Tired Front Lawn
100 ft × 50 ft of existing turf, perennial ryegrass overseeding rate 4.5 lb per 1,000 sq ft
Example 3 — Metric Lawn in Square Metres
20 m × 15 m of new tall fescue, entered in metric units
Example 4 — How Far Will One Bag Go?
A 50 lb bag of Kentucky bluegrass at the 2 lb per 1,000 sq ft new lawn rate
❓ Frequently Asked Questions
🔗 Related Calculators
How much grass seed do I need per 1,000 square feet?
It depends on the species. Kentucky bluegrass needs about 2 lb per 1,000 sq ft for a new lawn, perennial ryegrass 7, tall fescue 8, fine fescue 5 and bermudagrass 1.5. Overseeding an existing lawn uses roughly half of each of those figures.
How much grass seed do I need for a 5,000 square foot lawn?
Multiply the rate by 5. A new tall fescue lawn at 8 lb per 1,000 sq ft needs 40 lb, Kentucky bluegrass at 2 lb needs 10 lb, and overseeding the same area with perennial ryegrass at 4.5 lb needs 22.5 lb of seed.
What is the formula for grass seed quantity?
Seed in pounds = rate in lb per 1,000 sq ft x area in sq ft / 1,000. For a 2,400 sq ft lawn at 8 lb per 1,000 sq ft, that is 8 x 2,400 / 1,000 = 19.2 lb of seed.
How do I convert a seeding rate to grams per square metre?
Multiply pounds per 1,000 square feet by 4.882. So 8 lb per 1,000 sq ft is 39.1 g per square metre, and 2 lb per 1,000 sq ft is 9.8 g per square metre.
Should I use a different rate for overseeding?
Yes, use about half the new lawn rate. Overseeding drops seed into existing turf that already holds most of the ground, so the full rate crowds the new seedlings without thickening the lawn. Tall fescue drops from 8 to 5 lb per 1,000 sq ft, ryegrass from 7 to 4.5.
What happens if I use too much grass seed?
Seedlings compete with each other for light, water and nutrients, so the stand comes up thin and weak rather than thick. Overcrowded seedlings are also far more prone to damping off disease and to collapsing during the first dry spell after germination.
How much area does a 50 pound bag of grass seed cover?
Divide the bag weight by the rate and multiply by 1,000. A 50 lb bag of Kentucky bluegrass at 2 lb per 1,000 sq ft covers 25,000 sq ft, while the same bag of tall fescue at 8 lb per 1,000 sq ft covers only 6,250 sq ft.
Why do bluegrass and ryegrass have such different rates?
Because of seed size. A pound of Kentucky bluegrass holds roughly two million seeds, while a pound of perennial ryegrass holds only about 230,000. To land a similar number of seeds per square inch you need far more weight of the larger seeded species.
What is pure live seed and why does it matter?
Pure live seed is purity multiplied by germination. A bag at 85 percent purity and 90 percent germination is 76.5 percent pure live seed, so a 50 lb bag contains only 38 lb of viable seed. Cheap bags with high inert matter cover far less ground than the weight suggests.
How do I calculate seed for an irregular lawn?
Split the lawn into rectangles, triangles and circles, work out each piece and add them up, then subtract beds, paths and the house footprint. Entering a length and width that only approximate the shape is the largest single source of error in a seed order.
Does this calculator work in metric units?
Yes. Switch the unit selector to metric and enter the lawn in metres and the seed in kilograms. The dimensions convert automatically, and every result shows both the imperial and metric figures alongside the rate in grams per square metre.
When is the best time to seed a lawn?
Cool season grasses such as bluegrass, ryegrass and fescue establish best in late summer to early autumn, when soil is warm and weed pressure is falling. Warm season grasses such as bermudagrass and zoysiagrass want late spring once soil temperature is reliably above 65 degrees Fahrenheit.