Softonic

Grass Seed Calculator

Step 1 / 3 Seed needed (lbs)
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Buying grass seed by guesswork means either a patchy, thin lawn or a half-used bag going stale in the shed. This calculator takes your lawn length and width, the seeding rate, and whether you are starting a new lawn or overseeding an existing one, then returns the total area, the pounds of seed required, the number of 50 lb bags to buy, and an optional cost estimate. New lawns need roughly twice the seed of an overseed, so the purpose you pick matters as much as the square footage.

How to calculate grass seed quantity

  1. 1

    Measure the lawn

    Length × width in feet. For irregular yards, split the area into rectangles and add them together.

  2. 2

    Pick purpose and rate

    A new lawn is seeded at about 5 lbs per 1,000 sq ft; overseeding an existing lawn uses about 3 lbs. Choosing "Overseeding" caps the rate at 3.

  3. 3

    We compute the seed

    Pounds = (area / 1,000) × rate. Bags = pounds ÷ 50, rounded up. Cost = pounds × your price per pound.

How much grass seed you actually need

The formula is straightforward once the seeding rate is fixed. Seed is sold and rated per 1,000 square feet, so the whole calculation hangs on two numbers: your lawn area and the rate for the job.

Pounds of seed = (area in sq ft ÷ 1,000) × rate in lbs per 1,000 sq ft

The rate is the part people get wrong. A brand-new lawn that has bare soil to cover needs a heavy rate so seedlings fill in before weeds do. An established lawn that just needs thickening (overseeding) uses far less, because the existing turf is already holding the ground.

Worked example

A 50 ft × 40 ft new lawn is 2,000 sq ft. At the new-lawn rate of 5 lbs per 1,000 sq ft:

  • Pounds = (2,000 ÷ 1,000) × 5 = 10 lbs
  • Bags = 10 ÷ 50 = 1 bag (50 lb bag)
  • At $4 per lb, cost = 10 × $4 = $40

The same lawn overseeded at 3 lbs per 1,000 sq ft needs only 6 lbs, roughly 40% less seed.

Typical seeding rates (cool-season grasses)

Grass type New lawn (lbs/1,000 sq ft) Overseed (lbs/1,000 sq ft)
Kentucky bluegrass 2–3 1–2
Perennial ryegrass 7–9 4–5
Tall fescue 6–8 3–4
Fine fescue 4–5 2–3
Mixed sun blend 4–6 2–3

Warm-season grasses (Bermuda, zoysia) are seeded much lighter, often under 2 lbs per 1,000 sq ft, so always check the bag label for your specific seed.

Pitfalls to avoid

  • Over-seeding does not speed things up. Crowded seedlings compete for water and light and end up weak and disease-prone. Stick close to the rate on the bag.
  • Buy by pure live seed, not bag weight. Cheap mixes are padded with inert filler and weed seed. Check the seed tag for germination and purity percentages.
  • Seed has a shelf life. Germination drops after the first year, so buy roughly what you need rather than stockpiling.
  • Cover the whole rate evenly. Spread half the seed walking north–south and the other half east–west to avoid stripes.

Frequently Asked Questions

Seed is rated per 1,000 sq ft, not per single square foot. A new lawn typically uses about 5 lbs per 1,000 sq ft and overseeding about 3 lbs. So a 2,000 sq ft new lawn needs around 10 lbs of seed.

A new lawn starts from bare soil and needs a heavy rate so seedlings cover the ground before weeds move in. Overseeding spreads seed over existing turf to thicken it, so it uses roughly half as much seed. Selecting “Overseeding” caps the rate at 3 lbs per 1,000 sq ft.

Bag sizes vary, but this calculator assumes 50 lb bags for the bag count. Many consumer bags are smaller (3, 7 or 20 lb), so divide the total pounds by your actual bag size if it differs.

Yes. Seeding far above the recommended rate crowds seedlings, which then compete for water and nutrients and grow thin and disease-prone. More seed does not mean a thicker lawn; the right rate spread evenly does.

The values you enter are sent to our server so the calculator can compute the result, and when you move between the steps of the calculator they are carried in the page link. They are not stored or shared.

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