Lawn Seed Calculator
The Lawn Seed Calculator estimates how much grass seed to buy based on your lawn area and seeding rate, whether you're overseeding an existing lawn or starting fresh. Works in U.S. or metric units. Because lawns are purchased by weight rather than exact area, the calculator scales your seeding rate to your precise lawn size instead of rounding to a fixed bag size — helping you buy close to what you'll actually use. The seeding rate itself is the biggest variable: grass species, whether you're overseeding or starting from bare soil, and your region's climate all shift the recommended rate, so check your seed product's label alongside the general guidance below.
Switch between U.S. Customary and Metric units.
How This Tool Works
Pick your units, then enter your lawn's length and width, and choose a seeding rate — lighter for overseeding an existing lawn, heavier for starting from bare soil.
Formula & Method
Seed needed = area × seeding rate. In U.S. units, rate is pounds per 1,000 sq ft (result in lbs); in metric, grams per square meter (result in kg).
Example Calculation
A 3,500 sq ft lawn being overseeded at a light 3.5 lbs per 1,000 sq ft needs 12.25 lbs of seed (3.5 × 3,500 ÷ 1,000). If that same lawn were started from bare soil at a heavier 8 lbs per 1,000 sq ft, it would need 28 lbs (8 × 3,500 ÷ 1,000). In metric, a 325 m² lawn seeded new at 35 g/m² needs about 11.38 kg of seed.
About the Lawn Seed Calculator
Grass seed is sold by weight, but a lawn is measured by area, and the bridge between the two is the seeding rate. That rate, printed on most bags as pounds per 1,000 square feet or grams per square meter, tells you how thickly to sow. This calculator multiplies your lawn area by the rate you choose and reports the weight of seed to buy. You enter the lawn length, the lawn width, and the seeding rate, and it returns the lawn area and the amount of seed in pounds, or in kilograms and grams if you work in Metric mode.
The seeding rate is the part that matters most, and it is not a single number. A thin overseeding pass to fill gaps in an existing lawn uses a lighter rate than starting from bare soil. The grass species matters, the seed mix matters, and whether the seed has a coating all change what the bag recommends. The tool's default is a middle value, and its help text suggests lighter amounts for overseeding and heavier ones for a brand-new lawn, but the instructions on your product always take priority.
Getting the quantity right has real consequences. Sow too little and the lawn comes in patchy, giving weeds room to establish. Sow too much and seedlings compete, grow spindly, and are more prone to disease in damp weather, while you also waste money. A reliable estimate lets you buy the right bag sizes in one trip, with a small reserve for re-sowing thin spots after the first few weeks.
When to Use It
Overseeding a thinning lawn
A homeowner has an 80 by 55 foot lawn that has thinned out under summer heat. They plan to overseed in early fall at a light rate, so they enter the area and a rate near the low end of the range to find out whether one large bag will do, or whether they need two.
Seeding a brand-new yard
After a house build, the back yard is bare dirt. The owner measures a 60 by 45 foot area and chooses a heavier rate suited to a new lawn. The weight from the calculator guides them toward a bag size and lets them confirm the cost before scheduling the work.
Fixing bare patches after a project
A contractor finishing a regrading job needs to restore a strip of lawn quickly. They enter the strip's length and width and the label's recommended rate, then use the weight to buy only what the area needs and avoid carrying partial bags back to the shop.
Planning a lawn in metric
A homeowner in a metric country measures 18 by 14 meters and finds a recommended rate in grams per square meter on the packaging. Switching to Metric mode lets them enter that rate directly and read the answer in kilograms, ready to match against the sacks sold locally.
How to Use It, Step by Step
- Choose U.S. or Metric. U.S. mode uses feet for the lawn and pounds of seed per 1,000 square feet. Metric mode uses meters and grams per square meter.
- Enter the Lawn length. For an irregular yard, treat it as a rectangle with the same area, or measure separate rectangles and run the tool for each.
- Enter the Lawn width in the same unit. Subtract areas that will not be seeded, such as the house footprint, patios, and garden beds, by shortening the dimensions or running separate sections.
- Read the label on the seed you intend to use and find its recommended rate for a new lawn and for overseeding. Packages differ, so use their numbers rather than a general rule.
- Type that rate into the Seeding rate field. The tool starts with 5 pounds per 1,000 square feet or 25 grams per square meter, and the help text suggests 3 to 4 (15 to 20 in metric) to overseed and 6 to 8 (30 to 40) for new turf.
- Calculate and read the Lawn area, so you can check it against what you expect, and then the Seed needed in pounds or kilograms.
- Round up to the next bag size available. Bags come in fixed weights, so choose the size that covers the result with some left over.
- Plan the sowing and aftercare: apply half the seed in one direction and half at right angles, and keep the surface moist until the seedlings establish.
Understanding Your Results
Lawn area is the length times the width. It is easy to overlook, but it is the best check on your measurement. A rectangle of 80 by 55 feet is 4,400 square feet, which is roughly a tenth of an acre. If the number is not close to what you expected, the usual causes are mixing units or measuring around trees and beds that should be excluded.
Seed needed is the area divided by 1,000, multiplied by the rate in pounds. In metric, the tool works in grams per square meter and displays both kilograms and grams. Neither figure includes a margin. Real jobs lose some seed to uneven spreading, wind, and birds, and some areas need a second pass, so many people buy a bit more than the calculation shows. Rounding up to the next available bag usually covers this.
To judge the plausibility of the answer, remember that 1,000 square feet at the default 5 pounds takes 5 pounds, and a typical suburban lawn of 5,000 square feet takes 25. Overseeding at 3 to 4 pounds per 1,000 takes about 15 to 20 pounds on a lawn of that size, and a new lawn at 6 to 8 takes 30 to 40. If you see a total outside that spread, recheck the rate field and the unit mode before you buy.
More Worked Examples
Overseeding in early fall
Scenario: U.S. mode, 80 ft by 55 ft lawn, rate of 3.5 lbs per 1,000 sq ft for overseeding.
Area = 80 times 55 = 4,400 sq ft. Seed = 4,400 divided by 1,000 times 3.5 = 15.4 lbs. The tool reports 15.4 lbs. Because seed is commonly sold in bags of fixed weights, a 20 lb bag would cover the job with about 4.6 lbs left over for touching up bare spots, while two 10 lb bags would fall short.
New lawn from bare soil
Scenario: U.S. mode, 60 ft by 45 ft yard, heavier rate of 7 lbs per 1,000 sq ft.
Area = 60 times 45 = 2,700 sq ft. Seed = 2,700 divided by 1,000 times 7 = 18.9 lbs. The tool shows 18.9 lbs, which fits within a 20 lb bag with a pound left over. At the default 5 lbs per 1,000 sq ft, the same yard would need 13.5 lbs, so the choice of rate moves the answer by more than five pounds.
Metric lawn, new versus overseed
Scenario: Metric mode, 18 m by 14 m lawn, comparing 35 g/m2 for new turf with 17 g/m2 for overseeding.
Area = 18 times 14 = 252 m2. At 35 g/m2, the seed is 252 times 35 = 8,820 g, shown as 8.82 kg. At 17 g/m2, it is 252 times 17 = 4,284 g, shown as 4.28 kg. The new lawn needs about double the seed, so the decision about whether to renovate or overseed is also a decision about cost.
Tips for Better Results
- Follow the label first. Seed mixes are formulated for sun, shade, wear, or drought, and each recommends its own rate. Use the calculator to scale that rate to your lawn, not to replace it.
- Test your spreader on a tarp or driveway if you are unsure of the setting. Adjust until the amount that comes out for a known area matches the rate, then lay the seed in two passes at right angles for even coverage.
- Sow at the right time for your grass type. Cool-season lawns are commonly seeded in early fall when the soil is warm and the air is cooler, while warm-season grasses are usually seeded in late spring once the soil has warmed up.
- Make good seed-to-soil contact. Rake lightly to loosen compacted ground, spread the seed, and cover with a very thin layer of soil or compost. Seed buried too deeply struggles to emerge.
- Keep the top of the soil damp as seedlings sprout. Short, light watering once or more a day in the early weeks works better than occasional soaking, because seeds that dry out after starting to germinate are lost.
- Check the germination percentage and the weed seed content on the tag. Cheap seed can contain filler and weed seeds, so a slightly higher price per bag often means more usable seed per pound.
Common Mistakes to Avoid
- Using the same rate for every grass type. Species differ in seed size, and the correct weight per area varies, so a rate that works for one mix may be too heavy or too light for another.
- Including the whole property area. Subtract the house, driveway, and planting beds, or you will buy seed for ground that will never grow grass.
- Seeding too thickly in the hope of faster results. Dense seedlings compete and can be more prone to disease, so stick to the recommended rate.
- Ignoring coated seed. Coating adds weight, so a bag of coated seed holds less actual seed than the same weight of uncoated seed, and the label rate is usually higher.
- Skipping soil preparation. Seed thrown on hard, thatchy, or weedy ground gives poor results regardless of how well you calculated the amount.
Assumptions and Limits
- The calculator treats the lawn as one rectangle with a uniform seeding rate. Irregular yards and mixed sun and shade areas are better handled by calculating each zone separately.
- Rates are inputs and not recommendations for your grass. The suggested ranges in the help text are general guidance, while your seed's label reflects the species, mix, and coating of the product.
- Metric and U.S. results come from the same area and rate logic. The tool converts internally, so small differences from rounding between the two modes are normal.
- Growing success depends on weather, soil, watering, and timing, none of which the tool models. For a large or valuable lawn, a local extension office or lawn professional can advise on species and dates for your area.
Key Terms
- Seeding rate
- The weight of seed applied per unit of area, usually written as pounds per 1,000 square feet or grams per square meter.
- Overseeding
- Spreading new seed over an existing lawn to thicken thin areas, typically at a lighter rate than a new lawn.
- Cool-season grass
- A grass type, such as fescue, ryegrass, or bluegrass, that grows best in cooler weather and is usually seeded in early fall.
- Warm-season grass
- A grass type, such as bermudagrass or zoysia, that thrives in heat and is generally seeded in late spring or early summer.
- Germination
- The process in which a seed absorbs water and starts to grow a root and shoot. The germination percentage on a label shows how many seeds are likely to sprout.
- Starter fertilizer
- A fertilizer formulated for new seedlings that is typically richer in phosphorus than regular lawn fertilizer.
Related guides
Frequently Asked Questions
How much seed do I need per 1,000 sq ft?+
Overseeding an existing lawn typically needs 3–4 lbs per 1,000 sq ft (about 15–20 g/m²), while a brand-new lawn from bare soil needs 6–8 lbs per 1,000 sq ft (30–40 g/m²).
Can I calculate grass seed in kg and grams per square meter?+
Yes — switch the unit toggle to Metric and enter your lawn in meters with the seeding rate in grams per square meter. The result is returned in kilograms.
When is the best time to seed a lawn?+
Early fall is generally best for cool-season grasses, while late spring works well for warm-season grasses — check what's recommended for your grass type and region.
Should I fertilize when seeding?+
A starter fertilizer applied at seeding often helps new grass establish faster, but follow product-specific application rates rather than your regular lawn fertilizer schedule.
What if my grass seed product recommends a rate outside the typical range?+
The field accepts 1–20 lbs/1,000 sq ft (5–100 g/m² in metric), but most rates fall between roughly 3–8 lbs/1,000 sq ft. Different grass types vary — fine fescue and Kentucky bluegrass, for example, call for different rates — so follow your specific product's label over a general rule of thumb.
Should I buy exactly the calculated amount of seed?+
Round up slightly. Seed bags come in fixed sizes (commonly 3, 7, 20, or 50 lb bags), so it's better to have a little extra on hand for touch-up spots or reseeding thin areas than to run short partway through the job.
How long does grass seed take to germinate?+
It depends on the species and conditions. Perennial ryegrass can sprout within a week or so, while Kentucky bluegrass is slower and can take two to three weeks or longer. Warm soil, steady moisture, and good seed-to-soil contact speed things along. Seedlings then need several more weeks before the lawn is ready for regular mowing or foot traffic.
How deep should grass seed be covered?+
Grass seed is small and does best near the surface. Many guides suggest covering it with no more than about a quarter inch of soil, or simply pressing it into loosened ground. Burying seed too deeply can prevent seedlings from reaching the light. A thin top-dressing of compost or peat helps hold moisture around the seeds and reduces losses to wind and birds.
Does coated grass seed change how much I need?+
Yes. Coating adds weight to the bag, so only part of the stated weight is actual seed. Manufacturers therefore set a higher rate by weight for coated products. Take the rate from the package, enter it in the Seeding rate field, and the calculator will scale it to your lawn. Do not apply the rate from an uncoated product to a coated one, or you may under-seed.
What is the best way to spread grass seed evenly?+
A broadcast or drop spreader gives the most even result. Set it to the rate on the bag, fill it with half of the seed, and walk the lawn in one direction. Then fill with the remaining half and cross over at right angles. For small patches, spreading by hand in two passes works well. Mark the edges and avoid overlapping so the stripes do not show later.
How often should I water newly seeded grass?+
Keep the top inch or so of the seedbed consistently damp, which for many lawns means light watering once or twice a day in dry weather until the seedlings are established. Soaking once a week is not enough early on, because the seeds sit near the surface and can dry out. After the grass has sprouted and begun to fill in, gradually water less often but more deeply.
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