Grass Seed & Fertilizer Calculator
Work out how much grass seed or fertilizer your lawn needs from its area — for new lawns or overseeding — and how much nitrogen a fertilizer bag supplies.
How to use
- 1Enter your lawn area (ft²).
- 2For seed choose the grass type and new lawn or overseeding; for fertilizer enter the N percentage from the bag (the first number of N-P-K).
How it's calculated
Seed = area ÷ 1,000 × rate (lb per 1,000 ft²). Fertilizer product = target N (lb per 1,000 ft²) ÷ (N% ÷ 100) × area ÷ 1,000. A common target is 1 lb of nitrogen per 1,000 ft² per application.
Frequently asked questions
What do the numbers on fertilizer bags mean?
N-P-K: the percentages of nitrogen, phosphate and potash by weight. A 20 lb bag of 25-0-5 contains 5 lb of nitrogen.
When should I seed?
Cool-season grasses in early autumn (or spring); warm-season grasses in late spring to early summer.
Can I use more seed for faster results?
Too much seed leads to crowded, weak seedlings. Stick to the recommended rate.