Grass Seed Calculator

Work out exactly how many pounds of grass seed to buy for your lawn. Uses per-species seeding rates for new lawns, overseeding and patch repair, then rounds up to whole bags so you never come up short mid-job.

Method reviewed by Plant Calculator Team·Updated August 2026

1. Lawn area to seed

Area Entry Method

Length

Width

Non-Seeded Area to Exclude (optional)

sq ft

2. Grass species & seeding purpose

Grass Species

Custom Rate Override (optional)

lb/1000ft²

3. Packaging & cost

Buffer Allowance

Bag Size

Price per Bag ($)

How this is worked out

Net Lawn Area = Gross Area − Excluded Area   ·   Seed Needed (lb) = (Net Area ÷ 1000) × Rate (lb/1000 ft²) × (1 + Buffer%)

Application rates are per 1,000 square feet, the standard unit turf seed labels use. New-lawn rates are higher than overseeding rates because bare soil needs full stand establishment, while overseeding only fills gaps in existing turf.

Assumptions

Seeding rates reflect commonly published university turfgrass extension ranges for each species, using the midpoint of the typical range.

Overseeding rates are lower than new-lawn rates because existing turf already covers part of the ground.

Patch repair uses the new-lawn rate, since bare patches behave like a small new-lawn seeding.

Bag purchase quantity always rounds up (ceiling) to the next whole bag so you do not run short.

Your seed bag's own label rate — calibrated to that product's germination and purity — always takes priority over this general estimate.

How to calculate grass seed: new lawns, overseeding & PLS math

Calculating the exact weight of grass seed required for a lawn project is crucial for turfgrass success. Applying too little seed leaves sparse, bare patches that are quickly overtaken by invasive crabgrass and dandelions; spreading too much seed causes intense seedling competition where crowded grass shoots starve each other of moisture and succumb to fungal damping-off disease.

The Seed Size Disparity: Seeds per Pound

Application rates by weight vary drastically across species because individual seed sizes differ by more than a factor of ten. A single pound of tiny Kentucky Bluegrass contains nearly ten times more individual seeds than a pound of large Tall Fescue seed:

Turfgrass Species Seeding Rates and Seed Counts
Turfgrass Species	Approx. Seeds / Lb	New Lawn (lbs / 1,000 sq ft)	Overseeding (lbs / 1,000 sq ft)
Kentucky Bluegrass (KBG)	2,177,000 seeds/lb	2.0 – 3.0 lbs	1.0 – 1.5 lbs
Turf-Type Tall Fescue (TTTF)	227,000 seeds/lb	6.0 – 8.0 lbs	3.0 – 4.0 lbs
Perennial Ryegrass	227,000 seeds/lb	6.0 – 8.0 lbs	3.0 – 4.0 lbs
Fine Fescues (Creeping/Chewings)	500,000 seeds/lb	4.0 – 5.0 lbs	2.0 – 3.0 lbs
Bermudagrass (Hulled)	1,780,000 seeds/lb	1.5 – 2.5 lbs	0.75 – 1.25 lbs
Centipedegrass	400,000 seeds/lb	0.25 – 0.5 lbs	0.15 – 0.25 lbs

The Pure Live Seed (PLS) Quality Factor

Commercial grass seed bags contain inert matter, crop seed, weed seed, and non-viable seeds. Agronomists calculate the true value and application rate using the Pure Live Seed (PLS) formula:

Pure Live Seed (PLS %) = [Purity (%) × Germination Rate (%)] ÷ 100

Adjusted Bulk Seed Needed (lbs) = Target PLS Weight ÷ (PLS % ÷ 100)

Example: A seed label listing 90% purity and 85% germination has a PLS of (90 × 85) ÷ 100 = 76.5% PLS. To apply 6.0 lbs of viable seed, you must broadcast: 6.0 ÷ 0.765 = 7.84 lbs of bulk product.

Seedbed Preparation & Soil-to-Seed Contact

Core Aeration & Dethatching (Overseeding): Before overseeding existing turf, run a core aerator across the lawn in two directions to pull 2 to 3-inch soil cores. Seed falling into aeration holes makes direct contact with moist soil, increasing germination rates from 30% to over 80%.
Starter Fertilizer (High Phosphorus): Broadcast a starter fertilizer (such as 18-24-6 or 10-20-10) at seeding time to provide rapidly available phosphate ($P_2O_5$) that accelerates embryonic root cell division during the first 21 days.

Three Worked Seeding Examples

1. New Tall Fescue Lawn (5,000 sq ft Bare Soil Preparation)

New lawn rate: 7.0 lbs / 1,000 sq ft. Total seed required = 7.0 × 5 = 35.0 lbs of seed. Buy one 25-lb bag + one 10-lb bag. Apply half (17.5 lbs) north-south, and half east-west with a rotary spreader.

2. Fall Overseeding of Thin Kentucky Bluegrass Lawn (8,000 sq ft)

Overseeding rate: 1.5 lbs / 1,000 sq ft. Total seed required = 1.5 × 8 = 12.0 lbs of KBG seed. Aerate first, broadcast seed, and topdress with 1/8" screened compost.

3. Patch Repair on High-Traffic Dog Spots (300 sq ft Total Bare Spots)

Using Perennial Ryegrass (rapid 5-day germination): 8.0 lbs / 1,000 sq ft × 0.3 = 2.4 lbs of seed. Rake spots with a garden bow rake, scatter seed, tamp firmly with your boot, and cover with clean wheat straw.

Common Grass Seeding Mistakes

Applying standard pre-emergent weed preventers at seeding: Pre-emergent herbicides (Prodiamine, Dithiopyr) stop all seed germination, killing your new grass seed. Use only seed-safe mesotrione (Tenacity) as a starter pre-emergent.
Burying grass seed too deep: Grass seeds require light to trigger phytochrome germination. Seed buried deeper than 1/4 inch runs out of stored endosperm energy before reaching the surface. Rake lightly to 1/8" depth.
Letting the seedbed dry out for even a few hours: Once germinated, embryonic radicle root hairs die within 2 hours of drying out. Water 2 to 3 times daily with light 5-minute mists until seedlings reach 2 inches tall.

Manage lawn health and fertility with our Lawn Fertilizer Calculator, Sod Calculator, and Soil Drainage Calculator.

Common questions

How much grass seed do I need per 1,000 square feet?

It depends heavily on species: Kentucky Bluegrass needs about 2–3 lb per 1,000 ft² for a new lawn, while Tall Fescue and Perennial Ryegrass need 6–8 lb, and fine-seeded species like Centipede need only 0.25–0.5 lb. Seed size varies enormously between species, which is why rates differ so much.

What is the difference between new-lawn and overseeding rates?

A new lawn is bare soil, so it needs a full seeding rate to establish complete coverage. Overseeding fills gaps in an already-established lawn, so it typically needs roughly half the new-lawn rate — existing grass already occupies most of the ground.

Should I follow this calculator or the rate on my seed bag?

Always defer to your seed bag's label rate when available. It is calibrated to that specific product's germination percentage and purity (Pure Live Seed). This calculator gives a reliable estimate for planning and budgeting before you buy.

Why isn't St. Augustine grass in the species list?

St. Augustine is a vegetatively propagated grass — it's established from sod, plugs, or sprigs rather than seed, so it has no standard seeding rate to calculate.