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Grass Seed Calculator

Work out how much grass seed to buy for a new lawn or for overseeding. It uses your lawn area and the seeding rate on the label.

Level: Grade 6

  • Common Core standard 6.RP.A.3Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.
Printable worksheet

Grass Seed Calculator

Know the answer you need? Pick an input to work backward.

Inputs
Units
Job

One acre is 43,560 ft².

Use the rate on the seed label. Fine seed such as bluegrass is often 1–3 lb; tall fescue or ryegrass is often 6–10 lb.

Result

Seed needed

35 lb

Sow about 35 lb of seed over 5,000 ft², or 4 bags of 10 lb.

Bags of 10 lb
4
In kilograms
15.88 kg
Rate used
7 lb per 1,000 ft²
Rate used, metric terms
34.18 g/m²

See the step-by-step solution ↓

Step-by-step solution

  1. Express the area in thousands of square feet, the unit the rate uses

    5,0001,000=5

  2. Multiply the thousands of square feet by the seeding rate to get the seed needed

    5×7=35 lb

  3. Divide by the bag size, then round up to whole bags

    3510=3.5=round up → 4

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find out how much grass seed, and how many bags, to buy for your lawn. Grass seed is spread at a rate printed on the bag. In the US that's usually pounds per 1,000 square feet; elsewhere it's grams per square meter. The right rate depends a lot on the kind of grass. Tiny bluegrass seeds go a long way. The larger seeds of tall fescue need several times the weight to cover the same ground. Once you know the rate, the amount to buy is one multiplication.

This calculator takes the lawn area and the new-lawn rate from the label. It can halve that rate for overseeding, which means thickening a lawn that's already growing but thin. It gives the weight of seed in both pounds and kilograms, and the number of bags to buy. It also shows the rate in the other unit system, so you can compare products labeled differently.

Where it's used

Why this math matters outside the classroom:

  • New lawns. A 2,000 ft² new lawn at a label rate of 8 lb per 1,000 ft² needs 2 × 8 = 16 lb of seed.
  • Overseeding. Overseeding the same 2,000 ft² at half that label rate takes 8 lb, so a smaller bag may be enough.
  • Bare patches. Homeowners repair a 10 × 15 ft bare patch by finding its 150 ft² area and scaling the label rate to that size.
  • Metric labels. Gardeners reading a rate in grams per square meter multiply it by the lawn area in m² and divide by 1,000 for kilograms.
  • Rate reasoning. Students scale a rate given per 1,000 ft² to a lawn of any size with a table of equivalent ratios.

Grade level and standards: Grade 6; Common Core State Standards for Mathematics 6.RP.A.3. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose US units (square feet, pounds) or metric units (square meters, grams and kilograms).
  2. Choose a new lawn on bare soil, or overseeding to thicken an existing lawn.
  3. Enter the lawn area and the new-lawn seeding rate printed on the seed bag.
  4. Enter the bag size, then read the weight of seed and the number of bags.

What the inputs mean

Job
Overseeding means sowing into a living lawn to fill thin patches. Grass is already there, so about half the new-lawn rate is a common starting point.
Lawn area
Measure only the area you'll seed. For an oddly shaped yard, split it into rectangles, work out each one and add them up.
New-lawn seeding rate
Enter the rate for starting a new lawn, even when overseeding. The calculator halves it for you. If the label gives a range, the higher end gives quicker, thicker cover and the lower end saves seed.

Formula and method

rate used = new-lawn rate × 0.5 (overseeding)   or   new-lawn rate (new lawn)
seed (lb) = area (ft²) ÷ 1,000 × rate (lb per 1,000 ft²)
seed (kg) = area (m²) × rate (g/m²) ÷ 1,000
bags = seed ÷ bag size, rounded up
1 lb per 1,000 ft² = 453.59237 g ÷ 92.90304 m² ≈ 4.8824 g/m²

The rate is the amount of seed per area from the bag. ft² is square feet, m² is square meters, and g/m² is grams per square meter.

US seed rates are given per thousand square feet. So the lawn area is first divided by 1,000, then multiplied by the rate. Metric rates are per square meter, so the area multiplies the rate directly. The grams are then divided by 1,000 to give kilograms.

The conversion between the two rate units comes from the exact definitions of the pound (0.45359237 kg) and the foot (0.3048 m). The bag count is rounded up, because seed is sold in whole bags. First, the calculator clears away tiny computer rounding errors. That way an exact answer isn't pushed up by one bag.

Worked example

You're seeding a new 5,000 ft² lawn with seed labeled at 7 lb per 1,000 ft², sold in 10 lb bags.

  1. Area in thousands: 5,000 ÷ 1,000 = 5.
  2. Seed: 5 × 7 = 35 lb.
  3. Bags: 35 ÷ 10 = 3.5, which rounds up to 4 bags.

Result: You need 35 lb of seed (15.88 kg), which is 4 bags of 10 lb. The rate is about 34.18 g/m² in metric terms.

Understanding the result

The weight is the seed you'll spread, not a promise of coverage. Whether seeds sprout and take hold depends on soil contact, watering and temperature. Those matter far more than putting down extra seed.

If you end up with a partly used bag, store it somewhere cool and dry. Many seed labels show a test date, and older seed tends to sprout less well.

Assumptions and limitations

  • The seeding rate from the label suits your grass type and conditions.
  • Overseeding uses half the new-lawn rate, a common rule of thumb.
  • Seed is spread evenly over the whole area entered.
  • Seeding rates differ widely between grass types and blends, so the default rate is only a placeholder.
  • The calculator doesn't judge whether seeding, sod or another approach suits your site or season.
  • Bare patches inside an existing lawn may need the full new-lawn rate. Enter those areas separately.

Frequently asked questions

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

It depends on the grass. Small-seeded grasses such as Kentucky bluegrass or bermudagrass are often sown at around 1 to 3 lb per 1,000 ft². Larger-seeded tall fescue and perennial ryegrass are often sown at 6 to 10 lb. Always start from the rate printed on your bag.

How much seed do I need for overseeding?

A common starting point is about half the new-lawn rate, because existing grass already covers much of the ground. Very thin areas may need more, and a nearly full lawn may need less.

How much seed do I need for an acre?

An acre is 43,560 ft², or 43.56 thousand square feet. Multiply that by the rate. At 7 lb per 1,000 ft², an acre needs about 305 lb of seed for a new lawn.

Does putting down more seed give a better lawn?

Not usually. Sowing far above the label rate crowds the seedlings. They then compete for light, water and nutrients. Good seed-to-soil contact and steady moisture matter more than extra seed.

How this calculator is checked

Method: Area × application rate; overseeding at half the new-lawn rate (common rule of thumb); exact pound and foot definitions for unit conversion. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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