Garden & Water Utilities
Lawn Seed PLS & Bag Calculator
Add up your lawn areas, enter the seed tag purity and germination, and get the pounds of bulk seed and number of bags for a pure-live-seed rate.
How the numbers work
Seeding rates are written as pounds of pure live seed (PLS) per 1,000 square feet. PLS fraction = purity × germination, both from the seed tag. Bulk seed to buy = (area ÷ 1,000 × rate) ÷ PLS fraction, then rounded up to whole bags.
Worked example from the extension text: 98% purity × 80% germination = 78.4% PLS, so 20 lb PLS needs 20 ÷ 0.784 = 25.5 lb of bulk seed.
Area formulas: rectangle = length × width; triangle = ½ × base × height; circle = π × radius². Split an irregular lawn into these pieces and add them up. For a blend, the mix is treated as one product: its PLS fraction is the share-weighted average of each component's purity × germination.
Label rate overrides the preset. The preset table holds new-lawn rate ranges for common species and is a starting point; your seed label or local extension office wins, and cultivar, season and site can change the right rate. The table does not include overseeding rates, so enter the overseeding rate from your label. Rates are for seed only; nothing here covers fertilizer or herbicide.
Sources: Texas A&M AgriLife Extension, Turfgrass Mathematics, PDF p. 10 (Seeding Rate Calculations, PLS formula) and PDF p. 11 (area formulas); Virginia Tech, Virginia Agronomy Handbook, SPES-299, Part III Turfgrass, Table 1 “Recommended seeding rates for common turfgrass species” (PDF and printed p. 67; rates in lb per 1,000 sq ft). Accessed 2026-09-30. Runs entirely in your browser; nothing is sent anywhere.