Grass Seed Calculator
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What Your Result Means
- Seed Needed (pounds): The total weight of grass seed required to cover your lawn at the selected seeding rate. This accounts for proper coverage density.
- Square Footage: Your lawn's total area in square feet, calculated from length and width. This is the base for all seeding calculations.
- Bags (5 lb): The number of 5-pound seed bags you need to buy. This rounds up to ensure you have enough seed (e.g., 11.5 pounds requires 3 bags).
- New Lawn vs. Overseeding: New lawns require 4 lb per 1000 sq ft for dense coverage. Overseeding uses 2 lb per 1000 sq ft because existing grass provides some coverage.
How This Calculator Works
You enter your lawn's length and width in feet. The calculator multiplies these to find total square footage, then applies your chosen seeding rate (4 lb per 1000 sq ft for new lawns, 2 lb per 1000 sq ft for overseeding). It assumes uniform lawn shape and that rates are approximate; actual needs depend on soil quality, climate, and grass type.
Quick Questions
Why does my seed calculator show a different amount than the bag label?
Seeding rates vary significantly by grass species (fescue, bluegrass, ryegrass, bermuda), seed purity, and germination rates. This calculator uses standard industry recommendations—always check your seed bag's label for the rate specific to that product and follow the manufacturer's guidance.
Should I buy exactly the amount calculated or a bit extra?
Buy at least the calculated amount, rounded up to whole bags. Many lawn care professionals recommend buying 10–15% extra to account for spillage, seeding gaps, and future touch-ups. The calculator rounds up to the nearest 5-lb bag to help with this.
Can I use this calculator for overseeding a patchy existing lawn?
Yes. Overseeding (2 lb per 1000 sq ft) is designed for sparse or thin areas in established lawns. If more than 50% of your lawn is bare, consider using the new lawn rate (4 lb per 1000 sq ft) for those sections, or consult a local extension service for guidance.
What grass type should I choose?
This calculator uses seeding rates that work across common cool-season grasses (fescue, bluegrass, ryegrass) and warm-season types (bermuda). Check your local university extension service or seed supplier for species-specific rates if you want to optimize further.
Does lawn shape matter—what if it's not a rectangle?
This calculator assumes a rectangular lawn. For irregular shapes, divide your lawn into rectangles, calculate each section, and add the results together. Or estimate an average length and width that approximates your total area.
What time of year is best for seeding?
The best timing depends on your grass type and climate. Cool-season grasses seed best in early fall or spring; warm-season types seed in late spring or early summer. Consult your local extension office for the ideal window in your region.
Sources
- Purdue Landscape Report — Lawn Seeding Rates (standard seeding rates for cool and warm-season grasses)
- Oregon State University Extension — Seeding Rates for Lawns (regional recommendations and species-specific guidance)
- The Lawn Institute — Grass Seed Information (industry standards and best practices)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.