How much grass seed do I need for a 50 × 40 ft lawn?
For the worked example (a 50 × 40 ft lawn, a label rate of 4 lb per 1,000 sq ft, 10 lb bags) the material list is Grass seed: 1 × 10 lb bag (calculated 8 lb, based on 4 lb / 1,000 sq ft label rate). Quantities to buy are whole units rounded up from the calculated amounts. Enter your own measurements in the calculator above for your exact list.
How to use this calculator
- Measure each rectangular lawn area, or enter the total area if you know it.
- Read the seeding rate and the bag weight from your seed’s label and enter them.
- Keep the extra allowance at 0, or add a little if you want a margin.
- Copy, print or share the seed weight and the number of bags.
How this is calculated
- Lawn area = sum of (length × width) for each area
- Seed weight = lawn area ÷ 1,000 sq ft (100 sq m in metric) × label seeding rate
- With allowance = seed weight × (1 + allowance ÷ 100)
- Bags = round up (with allowance ÷ bag weight)
Geometry is deterministic. Material coverage, density, installation waste and product yield can vary. We expose those assumptions so you can replace them with the values printed on the products you are actually buying. Treat every result as an estimate. Items on your list are labelled Calculated (straight from your measurements) or Estimated (depends on an assumption), and “Buy” quantities are whole units rounded up.
Sources
No third-party figure is built into this calculator. Quantities come from geometry and from the values you can see and edit under “Assumptions” below, each labelled by where it comes from.
Last reviewed: . See the methodology.
Assumptions
These starting values are used until you change them. They are typical, not universal. Check the label on the product you are buying.
| Assumption | Starting value | Where it comes from |
|---|---|---|
| Seed weight | area ÷ 1,000 × label rate | Mathematical – Label rates are written per 1,000 sq ft (or per 100 sq m); the planner converts units for you |
| Seeding rate on the label | You enter it | You enter it (product / supplier) |
| Bag weight | You enter it | You enter it (product / supplier) |
| Extra allowance | 0% | Common planning default |
Worked example
A 50 × 40 ft lawn, a label rate of 4 lb per 1,000 sq ft and 10 lb bags:
- Grass seed: 1 × 10 lb bag (10 lb supplied) · 4 lb / 1,000 sq ft label rate
Common questions
What seeding rate should I use?
The one on your seed’s label. Rates vary by product and by whether you are seeding a new lawn or overseeding, and we do not recommend one.
Does it use metric rates?
Yes. In metric the rate is kilograms per 100 square meters, converted with the same unit table as everything else, so imperial and metric give the same answer.
Does it pick a grass type or a seeding time?
No. It is a quantity calculator for the seed you have chosen.