Grass Seed Calculator

The short answer

Seeding a new lawn takes roughly 6 to 8 pounds of tall fescue seed per 1,000 square feet, so a 5,000 square foot lawn needs 30 to 40 pounds. Overseeding an existing lawn uses about half that, 3 to 4 pounds per 1,000 square feet. Germination typically takes 7 to 21 days depending on species and soil temperature.

What it depends on

Species is the main variable, and the rate on the bag should override any general figure — Kentucky bluegrass, ryegrass, fescue and warm-season grasses all differ, and mixtures are seeded at the mixture rate. Autumn is the best seeding window in most climates because weeds are less competitive and the soil is still warm. Seed-to-soil contact matters more than the rate, which is why raking and rolling after sowing changes the result more than adding seed.

Where this stops being useful

This is a quantity estimate and does not cover soil preparation, amendments, starter fertiliser or irrigation, which usually matter more than the seed itself. Water restrictions in some regions affect establishment. Local extension guidance is the best source for species and timing in your area. General information and planning only, not engineering, structural or code advice.

The bag states a coverage rate, and that rate assumes a prepared seedbed — soil worked to a fine tilth, raked smooth, with the seed pressed into contact. Put seed onto hard ground or into existing thin turf and you will get a fraction of the result, which is the usual reason a new lawn looks patchy. Mixing a fast-germinating seed with a slower, harder grass is worth doing because the quick one holds the soil while the slow one fills in. Watering matters more than anything else: seed that dries out after germination does not come back.

Lawn projects go wrong in the preparation rather than the seeding, and the seed rate is the part people get right by reading the bag. Spreading a small area by hand is a different job from a full lawn, and the coverage rate assumes a broadcast spreader rather than a handful at a time.

Seed rate, lawn area and the matching fertiliser plan are linked. A newly seeded area needs feeding at seeding and again after the first flush of growth, and the timing is in weeks rather than months. When you order, check the seed date — old seed loses viability, and a bag that has been in a warm shed since last year can fail to germinate at all. Order enough for the area plus ten percent, since re-seeding a thin patch later means buying a small packet at full price.

Grass seed is sold by weight, and the quantity you need depends on whether you are starting a lawn from bare soil or thickening an existing one. A new lawn needs considerably more seed than overseeding, because every square foot must be colonised from scratch, while overseeding only fills gaps between established plants that are already doing most of the work. The standard rates are a useful guide. Roughly four pounds per thousand square feet suits a new lawn with good soil and careful watering; overseeding calls for about half that, and repairing bare patches needs a heavier rate to give the new grass a chance against competition. These figures assume decent seed and good conditions — thin soil, shade or a poor seedbed may need more, and buying cheap seed with low germination simply multiplies the quantity you need. Timing and contact with soil decide success more than quantity. Seed scattered on a hard, bare surface is food for birds; the same seed raked into the top quarter-inch and kept damp will germinate. Consistent moisture for the first two or three weeks matters more than any other single factor, and a seed-to-soil contact using a light raking, rolling or a dedicated overseeder transforms the results. This calculator applies the rate for your type of job to your measured area and rounds up to a purchase quantity. It assumes an even spread and average conditions, and it does not account for slope or heavy shade, both of which warrant extra seed. Divide the lawn into manageable sections and weigh out the seed for each, so no area is over- or under-sown.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.