Grass Seed Calculator
Estimate grass seed for a new lawn or overseeding. Use your product label to find seed to apply, whole bags to buy, leftover, and optional cost.
Full Grass Seed GuideTransparent methodology
How the grass seed estimate is calculated
1. Measure the lawn
Add non-overlapping lawn sections. Rectangles use length × width, circles use π × (diameter ÷ 2)², and triangles use base × perpendicular height ÷ 2. Subtract only excluded areas included in those measurements.
2. Read the product label
Choose coverage per bag or an application rate. Use the new-lawn or overseeding value appropriate to your project. The calculator does not choose a grass species or recommend a universal rate.
3. Calculate seed to apply
Multiply net area by the rate using consistent units. If you enter bag coverage and weight instead, divide net area by coverage and multiply by bag weight.
4. Plan the purchase
Add an optional reserve once, then round upward to whole bags. Cost is whole bags × price per bag. Reserve and packaging surplus remain separate from the amount to spread. Tax, delivery and labor are excluded.
Worked example
For 4,500 ft² at an entered rate of 4 lb per 1,000 ft², apply 18 lb. With no reserve and 10 lb bags, buy 2 bags (20 lb), leaving 2 lb. At $35 per bag, the bag cost is $70. These are illustrative inputs, not a recommended rate.
Answers before you order
Frequently asked questions
How much grass seed do I need?
Use the coverage or application rate printed on your seed bag for your project. Enter the lawn area, subtract any included paths or beds, and apply that rate. There is no single rate that is appropriate for every grass mixture.
How do I calculate grass seed for overseeding?
Select Overseeding and enter the product’s overseeding coverage or rate. Switching project type does not automatically halve the rate. Verify the label value yourself before calculating.
How many bags should I buy?
The calculator divides the required quantity, including any selected reserve, by the coverage or weight of one bag and rounds upward. A partial bag requirement still requires a whole bag purchase.
Can I calculate from square feet or acres?
Yes. Enter known area in square feet, square meters, acres or hectares. You can also measure rectangles, circles and triangles in feet or meters and add multiple non-overlapping sections.
How much does a 50 lb bag cover?
Coverage depends on the specified seeding rate. For an illustrative rate of 5 lb per 1,000 square feet, 50 lb covers 10,000 square feet. Use the actual rate for your product and project rather than treating this example as a recommendation.
Should I spread the extra seed left in the bag?
Not automatically. The amount to apply follows the entered label rate. Optional purchase reserve and whole-bag rounding can leave surplus; they do not change the application rate for your measured lawn.
Why is the seed weight unknown?
Bag coverage can determine the number of bags without revealing their weight. Add the matching bag weight in Advanced options to calculate pounds, kilograms and estimated leftover.
For seed-label background, see University of Minnesota’s seed-buying guidance. Local advice may differ; always check the product label and conditions at your site.
Need another project tool?