Lawn Seed & Fertiliser Spreader Calculator
Calculate grass seed pounds, NPK fertiliser weight, and bag requirements for new lawn establishment or overseeding with spreader settings.
Lawn & Turf Specifications
Application & Spreader Guide
Turfgrass Seeding Rate Reference (per 1,000 sq ft)
About this tool
How to use it
- Choose your measurement system (US Customary in feet/lbs or Metric in meters/kg).
- Enter your lawn dimensions (Length × Width), total square footage/m², or acreage.
- Select your turfgrass variety (Kentucky Bluegrass, Tall Fescue, Ryegrass, Fine Fescue, Bermuda, Zoysia, Centipede) and purpose (Overseeding vs. New Lawn).
- Select your fertilizer N-P-K grade and target Nitrogen application rate, then click Calculate Seed & Fertilizer to view total weight, suggested bag purchases, and spreader instructions.
Why it matters
Under-seeding results in thin, weed-prone turf, while over-seeding creates crowded seedlings that compete for moisture and succumb to fungal damp-off disease. Applying fertilizer accurately prevents nitrogen burn and runoff while delivering the exact university-extension recommended nutrient dosage.
When to use it
Use this calculator during late summer/early fall overseeding season, spring lawn wake-up feeding, when renovating bare patches, or before buying seed and fertilizer bags at the home improvement center.
Good to know
Calculations use agronomic turfgrass extension seeding standards (e.g. Kentucky Bluegrass at 2.5 lbs/1k new or 1.25 lbs/1k overseed; Tall Fescue at 8.0 lbs/1k new or 4.0 lbs/1k overseed). Fertilizer calculations use standard guaranteed analysis N = Target N / (%N / 100) * (Area / 1000).
Common questions
What is the best time of year to seed and fertilize a lawn?
For cool-season grasses (Kentucky Bluegrass, Fescue, Ryegrass), late summer to early fall (mid-August to late September) is optimal because soil temperatures are warm and weed competition is low. For warm-season grasses (Bermuda, Zoysia, Centipede), late spring to early summer (May to June) yields the fastest establishment.
What is the difference between seeding a new lawn versus overseeding?
New lawn establishment on bare prepared soil requires 100% full seeding density because there is no existing root structure. Overseeding an existing lawn requires 50% of the full seeding rate to thicken sparse turf without over-crowding the existing grass canopy.
How do you calculate fertilizer bag coverage from the N-P-K numbers?
Divide your target nitrogen rate (usually 1.0 lb N per 1,000 sq ft) by the first number on the bag divided by 100. For example, a 24-0-4 fertilizer contains 24% nitrogen, so 1.0 ÷ 0.24 = 4.17 lbs of fertilizer per 1,000 sq ft. A 5,000 sq ft lawn requires approximately 20.8 lbs of bulk fertilizer.
Should you apply fertilizer at the same time as grass seed?
Use a specialized starter fertilizer high in phosphorus (such as 24-25-4 or 18-24-12) at the time of seeding to promote rapid seedling root development. Avoid high-nitrogen quick-release fertilizers or weed-and-feed products containing pre-emergent herbicides, which inhibit grass seed germination.
How should I set my rotary or drop spreader?
To ensure uniform coverage without streaks or missed strips, set your spreader to half the recommended rate and make two perpendicular passes over the lawn in a cross-hatch pattern (north-south, then east-west).