Lawn Seeding Rate Calculator
Calculate how much grass seed you need based on your lawn area, grass species, and whether you are seeding a new lawn or overseeding an existing one.
Formula
Step 1 — Pure Live Seed (PLS):
PLS (%) = (Germination % / 100) × (Purity % / 100)
Step 2 — Adjusted Seeding Rate:
Adjusted Rate (lbs/1,000 sq ft) = Base Rate (lbs/1,000 sq ft) ÷ PLS
Step 3 — Total Seed Required:
Total Seed (lbs) = Adjusted Rate × (Lawn Area in sq ft ÷ 1,000)
The PLS adjustment ensures you apply enough viable seed regardless of the germination and purity printed on the seed label. A bag with 85% germination and 95% purity has a PLS of 80.75%, meaning only ~81% of the seed by weight is capable of producing a plant.
Assumptions & References
- Base seeding rates are per 1,000 sq ft and sourced from university cooperative extension guidelines (Purdue University, Penn State Extension, NC State Extension, University of Georgia Extension).
- Overseeding rates are set at 50% of new-lawn rates, consistent with standard turfgrass management practice.
- Pure Live Seed (PLS) methodology follows USDA Natural Resources Conservation Service (NRCS) seeding rate standards.
- 1 acre = 43,560 sq ft; 1 sq meter = 10.7639 sq ft; 1 lb = 0.4536 kg.
- Germination and purity percentages should be read from the seed label's "Guaranteed Analysis" section.
- Rates assume broadcast or drop spreader application on prepared seedbed; hydroseeding or slit-seeding may use different rates.
- Environmental factors (soil temperature, moisture, shade) affect actual establishment and are not included in this calculation.
- Bag quantity estimates are rounded up to the nearest whole bag to ensure sufficient coverage.