How to Measure Your Lawn for Grass Seed

Why Accurate Measurement Matters

Before you buy a single bag of grass seed, you need to know your lawn's square footage. This one number determines everything: how many pounds of seed to buy, how much starter fertilizer to apply, and how long the job will take. Getting it wrong in either direction costs you.

• Too little seed: You run short mid-project, face a second trip to the store, and risk bare patches that weeds will colonize before the grass can fill in.
• Too much seed: Grass seed has a shelf life. Unused bags stored in a garage for a year often have significantly reduced germination rates. Buying a 50 lb bag when you need 18 lbs means paying for roughly $40–$80 in seed you'll likely throw away.

Accurate measurement also matters for soil amendments. Starter fertilizer labels list rates per 1,000 square feet. Overseeding an aerated lawn requires lime or gypsum in precise quantities. Every product on the shelf assumes you know your square footage — so measure first, then shop.

How to Measure a Simple Rectangular Lawn

For a straightforward rectangular yard, the calculation is basic geometry:

Area (sq ft) = Length (ft) × Width (ft)

Walk your lawn with a 100-foot measuring tape or a measuring wheel. Measure the longest dimension from edge to edge — call that your length. Then measure the perpendicular dimension — your width. Multiply the two numbers.

Example: A backyard measuring 60 feet long by 40 feet wide is 2,400 sq ft.

If your tape measure is only 25 feet, measure in segments and add them together. A measuring wheel (available at hardware stores for under $30) makes this faster and handles gentle curves reasonably well.

How to Measure Irregular or L-Shaped Lawns

Most residential lawns are not perfect rectangles. Front yards often have angled property lines; backyards have deck cutouts, garden wings, or irregular corners. The trick is to break the space into smaller rectangles, measure each one, and add them together.

The Rectangle-Splitting Method

Stand at one corner of your yard and visualize where you could draw a straight line to split the space into two (or three) simpler rectangles. Measure each rectangle separately. Add the totals.

Example — L-shaped backyard:

• Main section: 50 ft × 35 ft = 1,750 sq ft
• Side wing: 20 ft × 15 ft = 300 sq ft
• Total: 2,050 sq ft

For yards with diagonal edges or curved sides, overestimate slightly by treating each curve as a rectangle, then subtract 10–15% to account for the curved portions. Or use GPS measurement (covered below) for precision without the guesswork.

How to Subtract Non-Lawn Areas

Your total yard square footage is not the same as your seeding area. Any space that won't receive seed must be subtracted before you calculate how much seed to buy. Common areas to exclude:

• Concrete or paver patios
• Driveways and sidewalks
• Garden beds and flower borders
• Mulched tree rings
• Play structures, sheds, or outbuildings with their footprint
• Gravel paths or dry creek beds

Measure each non-lawn area the same way — length × width for rectangles. For a circular tree ring, use the formula Area = π × radius² (roughly 3.14 × radius × radius). A 4-foot radius tree ring is about 50 sq ft.

Example: Your total backyard is 2,400 sq ft. You have a 12 × 14 ft patio (168 sq ft), a 10 × 6 ft garden bed (60 sq ft), and two tree rings at roughly 50 sq ft each. Total non-lawn: 328 sq ft. Seedable lawn area: 2,072 sq ft.

Grass Seed Coverage Rates by Grass Type

Once you know your square footage, use the table below to determine how many pounds of seed you need. Coverage rates differ for new lawn establishment (bare soil) versus overseeding (filling in thin or patchy existing turf). New lawn rates are higher because you need full, dense coverage from scratch. Overseeding rates are lower because existing grass provides some ground cover.

Grass Type	New Lawn (lbs / 1,000 sq ft)	Overseeding (lbs / 1,000 sq ft)
Kentucky Bluegrass	2 – 3 lbs	1 – 1.5 lbs
Tall Fescue	6 – 8 lbs	3 – 4 lbs
Bermuda (hulled)	1 – 2 lbs	0.5 – 1 lb
Zoysia	1 – 2 lbs	1 – 2 lbs
Perennial Ryegrass	8 – 10 lbs	4 – 5 lbs

These rates are for pure seed. Many bags sold at home improvement stores are "mixes" — for example, a Sun & Shade mix might combine Kentucky Bluegrass, Perennial Ryegrass, and Fine Fescue. Follow the label rate on the specific bag if it differs from the table above.

Always buy 10% more than your calculation suggests. Seed distribution from a spreader is never perfectly uniform, and having a small reserve lets you touch up thin spots after germination without a second purchase.

New Lawn vs. Overseeding: Key Differences

New Lawn Establishment

Starting from bare soil requires the higher seeding rates in the table above. Before spreading seed, the soil should be tilled 2–4 inches deep, raked smooth, and — ideally — tested for pH. Most cool-season grasses prefer a pH of 6.0–7.0. Seed-to-soil contact is critical: a light rake after seeding or a slit-seeder machine will dramatically improve germination rates compared to broadcasting onto an untilled surface.

Timing for new lawns: early fall (late August through September) for cool-season grasses like Fescue, Bluegrass, and Ryegrass. Late spring through early summer for warm-season grasses like Bermuda and Zoysia, once soil temperatures are consistently above 65°F.

Overseeding an Existing Lawn

Overseeding thickens a thin lawn or introduces improved grass varieties without full renovation. Because existing grass covers part of the soil, seed-to-soil contact is lower — which is why overseeding uses roughly half the seed rate of new establishment. To improve results:

• Mow existing grass short (1.5–2 inches) before seeding
• Core aerate to open up soil channels for seed to fall into
• Rake up clippings so seed can reach the soil surface
• Apply a starter fertilizer at the time of seeding
• Water lightly and frequently (2–3 times daily) until germination, then reduce frequency

The best time to overseed cool-season lawns is early fall — soil is still warm from summer (which speeds germination) but air temperatures are cooler (which reduces competition from crabgrass and other summer weeds).

Step-by-Step Calculation Example

Let's walk through a complete example so you can apply the same process to your own yard.

Scenario: You have a 2,400 sq ft backyard. After subtracting a patio (200 sq ft) and a garden bed (120 sq ft), your seedable lawn area is 2,080 sq ft. You want to overseed with Tall Fescue.

• Overseeding rate for Tall Fescue: 3–4 lbs per 1,000 sq ft
• Your lawn: 2,080 sq ft ÷ 1,000 = 2.08 (thousands of sq ft)
• Seed needed (low end): 2.08 × 3 lbs = 6.24 lbs
• Seed needed (high end): 2.08 × 4 lbs = 8.32 lbs
• Add 10% buffer: 8.32 × 1.10 = 9.15 lbs

Round up to the nearest standard bag size. A 10 lb bag of Tall Fescue covers this project with a small reserve. If your local store only carries 7 lb bags, buy two (14 lbs) — you'll have enough for a second pass over any thin spots.

Using GPS to Measure Odd-Shaped Lawns

Tape measures work for rectangles. They become slow and error-prone when your lawn has curves along a fence line, slopes across a hillside, wraps around a house corner, or follows an irregular property boundary. Every offset measurement introduces compounding errors.

A faster and more accurate approach for complex lawns is GPS-based measurement. LandLens lets you walk the perimeter of your lawn with your iPhone in hand. As you walk, the app traces your path using GPS and calculates the enclosed area in real time. When you close the polygon by returning to your starting point, you have the exact square footage displayed on screen — no math required.

LandLens is especially useful when:

• Your yard has curves along a fence, wall, or garden border
• The terrain slopes significantly, making tape measurement difficult
• You need to measure around obstacles like trees, sheds, or HVAC equipment
• You want to measure individual zones (front yard, back yard, side strip) separately
• You need to subtract interior features by tracing their perimeter individually

After walking the boundary, you can subtract non-lawn areas by tracing them as separate polygons. The app handles the subtraction automatically. The whole measurement process for an average residential lot takes under five minutes.

LandLens — Land Area Measure & GPS is available on the App Store. Measure your lawn before you leave for the garden center, and you'll know exactly how many bags to put in your cart.

Frequently Asked Questions

How many square feet does a 50 lb bag of grass seed cover?

It depends entirely on the grass species. A 50 lb bag of Tall Fescue at a new-lawn rate of 7 lbs per 1,000 sq ft covers approximately 7,100 sq ft. The same 50 lb bag of Perennial Ryegrass at 9 lbs per 1,000 sq ft covers only about 5,600 sq ft. For overseeding, those same bags cover roughly twice the area. Always check the label on the specific bag — seed companies print recommended coverage rates for their product blend.

Should I measure before or after removing dead grass?

Measure your total lawn area before removing dead grass or thatch. The square footage of your turf does not change because you dethatched or scalped it — the underlying soil surface is the same. Measuring first saves time and lets you calculate seed needs before you start any physical prep work. What does change is whether you use new-lawn rates or overseeding rates: if you're removing all existing vegetation and starting fresh, use the higher new-lawn rate. If you're renovating over existing soil with some living grass remaining, use the overseeding rate.

How much does it cost to reseed a lawn?

DIY reseeding costs primarily come from seed, fertilizer, and soil amendments. For a 2,000 sq ft lawn overseeded with Tall Fescue, expect to spend roughly $40–$80 on seed, $20–$40 on starter fertilizer, and $0–$50 on soil amendments depending on your soil condition. Core aeration rental runs $70–$100 for a half-day. Total DIY cost for a 2,000 sq ft overseeding project: $130–$270. Professional lawn renovation services (full slice-seeding with prep) typically run $0.08–$0.20 per square foot, so a 2,000 sq ft lawn would cost $160–$400 professionally — not counting any soil amendment or fertilizer costs the contractor may add.