How Much Grass Seed Do I Need?

The rate belongs to the seed, not to the lawn

New lawn, pounds per 1,000 sq ft:

Grass	Rate
Tall fescue	8–10
Perennial ryegrass	7–8
Kentucky bluegrass	2–3

Bluegrass isn't a quarter of the rate because you need a quarter of the grass. It's because the seeds are tiny:

	Seeds per pound
Kentucky bluegrass	~2,200,000
Tall fescue	~230,000

Nearly ten times as many seeds in the same weight. Rates are quoted by weight only because weight is how seed is sold.

But the rates don't equalise the seed count

This is the part I expected to find and didn't. Work it through per square foot:

At its own rate	Seeds per sq ft
Tall fescue, 9 lb/1,000	2,070
Kentucky bluegrass, 2.5 lb/1,000	5,500

Bluegrass goes down at two and a half times the seed density — on a quarter of the weight. That holds across the whole published range: 2.4× at the low ends, 2.9× at the high ones.

So the tidy explanation — small seeds, so less weight for the same coverage — is wrong. Bluegrass is deliberately sown thicker.

The reason is that it establishes completely differently. Bluegrass seedlings are very small and slow to get going, and a mature bluegrass lawn fills in by spreading through rhizomes rather than by every seed becoming a plant. It's sown thickly and thins itself out.

Tall fescue is a bunch grass that barely spreads sideways at all. Each of its seeds has to count.

Either way the practical rule survives: applying a bluegrass rate to a fescue bag under-seeds badly, and a fescue rate to bluegrass buries it.

The arithmetic

Area ÷ 1,000 × rate.

Enter the length and width of the lawn and the seeding rate. A lawn 60 ft long by 40 ft wide is 2,400 sq ft; at 5 lb per 1,000 that is 12 pounds.

Measure an irregular lawn as several rectangles and add the areas — don't use the bounding box, which includes beds, paths and driveway you aren't seeding.

Everything difficult about this is choosing the rate. The multiplication isn't the problem.

Overseeding is about half

Grass	New lawn	Overseeding
Tall fescue	8–10	4–6
Perennial ryegrass	7–8	3–4
Kentucky bluegrass	2–3	1–2

Different job. You're threading new grass into an existing canopy rather than establishing one on bare soil, so there's less light and less room per seedling.

Applying a full new-lawn rate over living turf smothers what you already have.

Use the rate on the bag

Above every table here, including this one.

Mixes are extremely common, and a mix's rate is not the average of its components' rates. The bag is written for the exact blend inside it, which no general table can be.

Use the table to plan before buying, or to sanity-check a bag whose claim looks odd. Once the bag is in your hand, its figure wins.

More seed is not insurance

This is one of the few garden calculations where over-ordering actively hurts.

Too much seed produces dense, spindly seedlings competing with each other for light, water and nutrients. The stand that results is genuinely weaker than a correctly seeded one — thinner, more disease-prone, and slower to fill in.

Buy what you need, apply the stated rate, and keep the surplus sealed for patching rather than spreading it because you have it.

What actually decides whether it grows

Three things this calculation says nothing about. All of them matter more than the rate:

Soil contact. Seed lying on top of thatch will not germinate. Rake or scarify first.

Timing. Most cool-season grasses go down in early autumn, not spring — warm soil, falling weed competition, and a whole cool season ahead before summer stress.

Water. New seed needs consistent moisture for weeks, and week two is when people stop paying attention. This kills far more new lawns than a slightly wrong rate ever has.

Leftover seed doesn't keep forever

Germination falls year on year, faster if it's been stored warm or damp.

Sealed, cool and dry, a leftover bag is usually fine next season for patching. A bag that's been open in a shed for two years is unreliable rather than free — and seeding a whole lawn is not where you want to discover that.

Print the seeding sheet — it has the rate table, a per-section area worksheet, and a checklist whose first item is read the rate off the bag.

Sources: Eartheasy — grass seed calculator · Columbia Seeds — turfgrass seeding rate chart