Grass Seed Calculator

Seed (lb) = seeding rate (lb per 1,000 ft²) × area (ft²) ÷ 1,000

r

Seeding rate for the species, per 1,000 square feet

A

Area of the lawn to be sown

k

Seeding method factor: 1 for a new lawn, 0.5 when overseeding

Use it before you order, not after. Seed is sold by weight in bags from 1 lb to 50 lb, and the spread between species is wide enough that guessing costs a second trip or leaves half a bag going stale in the shed. A new lawn takes the full rate, overseeding takes half of it, and a lawn being repaired after winter or sown late in the season wants the higher end of its range.

1. A 5,000 ft² new lawn of tall fescue

   1. Tall fescue is seeded at 7 lb per 1,000 ft²
   2. Area: 5,000 ft², which is 5 units of 1,000 ft²
   3. Seed: 7 × 5 = 35 lb
   4. In metric: 35 lb = 15.88 kg
   5. The same rate in metric: 34.2 g per m²

   35 lb is most of a 50 lb bag. Seed loses germination in storage — a bag left open in a hot shed over a summer can drop several points — so buy close to the day you sow and keep what is left sealed and cool rather than carrying it over to next spring.

2. The same 5,000 ft², overseeded instead

   1. Overseeding takes half the new-lawn rate: 7 ÷ 2 = 3.5 lb per 1,000 ft²
   2. Seed: 3.5 × 5 = 17.5 lb
   3. In metric: 17.5 lb = 7.94 kg
   4. Rate in metric: 17.1 g per m²

   Half, not three quarters: the established grass is still there and the seed only has to fill the gaps between it. Buying the new-lawn rate for a top-up dressing is the most common way to spend twice what the job needs.

3. 10,000 ft² of bermudagrass, a warm-season lawn

   1. Bermudagrass is seeded at 1.5 lb per 1,000 ft²
   2. Area: 10,000 ft², which is 10 units of 1,000 ft²
   3. Seed: 1.5 × 10 = 15 lb
   4. In metric: 15 lb = 6.8 kg
   5. Rate in metric: 7.3 g per m²

   Bermudagrass takes 1.5 lb per 1,000 ft² against tall fescue's 7, so twice the area needs less than half the seed. The rate belongs to the species and not to the size of the seed — which is why the table below is the more useful half of this page.

The rates are typical figures, not a standard: they move with the cultivar, the region, the seed lot, and above all with whether the seed is coated. Coated and pelleted seed carries a substantial share of inert material by weight, so two bags of the same weight can hold very different amounts of live seed. No single authority publishes one table — extension services in neighbouring states disagree by 20% or more — so treat these as magnitudes and check the bag or your local recommendation. Seeding into bare soil takes the full rate, overseeding takes half, and a slope, a late sowing or a lawn being raced against weeds wants more than either. Hand-broadcasting rarely spreads evenly, which is why most people sow 10% to 20% over the calculated figure. There is no bag count here: bags come in every size from 1 lb to 50 lb, and a bag count would only be right for one of them.

How much grass seed do I need per square foot?

It depends on the species: tall fescue takes 7 lb per 1,000 square feet, perennial ryegrass 6, Kentucky bluegrass 2, bermudagrass 1.5 and zoysia 1. Per square foot that is 0.001 to 0.007 lb, which is why the rate is always quoted per thousand rather than per one.

How much seed do I use when overseeding?

Half the new-lawn rate. On the same 5,000 ft² lawn that is 17.5 lb of tall fescue instead of 35. The existing grass still covers the ground, so the seed only has to fill the gaps and thicken what is already there.

How do I work out the lawn area?

Multiply the length by the width for each rectangle and add them up: a 50 ft by 100 ft lawn is 5,000 ft². An irregular lawn is easier to break into two or three rectangles than to measure as one shape, and a curved bed can be measured as the rectangle it fits inside, minus about a quarter.

Does coated seed change the amount I need?

Yes, upweight it. Coated and pelleted seed carries a significant share of inert material by weight, so a pound of coated seed contains noticeably less live seed than a pound of raw seed. Where the bag states a coating percentage, divide the rate by the live-seed fraction rather than guessing.

Why does the calculator not give a number of bags?

Because there is no standard bag. Grass seed is sold in bags from 1 lb to 50 lb, and a bag count would be right for exactly one of them. The weight is what you order and what the label is written in, so that is what this page returns.

Which grass seed should I choose?

Cool-season grasses — tall fescue, Kentucky bluegrass, perennial ryegrass — are the ones for northern lawns, and warm-season grasses such as bermudagrass and zoysia take over in the south. The species decides the seeding rate as well as the look of the lawn: bermudagrass is sown at 1.5 lb per 1,000 ft² where tall fescue needs 7.

• Approximate Conversions from U.S. Customary Measures to Metric — the chart behind the pound, kilogram, square foot and square metre conversions used here — National Institute of Standards and Technology
• The International System of Units (SI) brochure — the kilogram and the square metre, the two units every figure on this page is converted into — Bureau International des Poids et Mesures (BIPM)