Free Landscape Calculator
Fertilizer Calculator
Calculate exactly how many pounds and bags of fertilizer you need based on lawn size, fertilizer type and nitrogen application rate. Instant results with cost estimates.
👤 Who is this for: homeowners, lawn-care DIYers & landscaping pros.
📊 Understanding Your Results
Pounds of Fertilizer — Total weight of fertilizer product needed to deliver the target nitrogen rate to your lawn area.
Bags to Buy — Number of bags needed rounded up. Store leftover fertilizer in a cool, dry location.
Cost Estimate — Based on average US fertilizer prices of $25–$45 per bag.
How the Fertilizer Calculator Works
Our fertilizer calculator uses the nitrogen content (first number in NPK) and your target nitrogen application rate to determine exactly how much product to apply.
The Fertilizer Formula
Step 2: Fertilizer (lbs) = (Area ÷ 1,000) × N Rate × (100 ÷ N%)
Step 3: Bags = Fertilizer lbs ÷ Bag size (round up)
Step 4: Never exceed 1 lb of nitrogen per 1,000 sq ft per application
Example: 5,000 sq ft, 10-10-10, 1 lb N rate = (5 × 1) × (100÷10) = 50 lbs = 1 bag of 50lb fertilizer. Cost = $28 (one 50-lb bag).
Fertilizer NPK Guide
| Fertilizer | N-P-K | Best For | Rate |
|---|---|---|---|
| All-Purpose 10-10-10 | Equal NPK | New lawns | 10 lbs/1,000 sqft |
| Slow Release 24-0-11 | High N | Established lawns | 4 lbs/1,000 sqft |
| High-Nitrogen 30-0-4 | 30-0-4 | Lawn greening | 3.3 lbs/1,000 sqft |
📝 Real Project Example
5,000 sq ft lawn, 24-6-6 fertilizer, standard 1 lb N rate:
- Nitrogen needed: 5 × 1 = 5 lbs of N
- Product needed: 5 ÷ 0.24 = 20.8 → 21 lbs (one 20-lb bag covers it)
- With 10-10-10 instead: 5 ÷ 0.10 = 50 lbs — higher N analysis means fewer bags to haul
- Cost check: one 20-lb bag of 24-6-6 at ~$25–$30 = ~$28 per application
Never exceed 1 lb of N per 1,000 sq ft in a single application — more burns the lawn and washes into waterways. Split the annual 2 lbs across spring and fall.
📚 Sources & Methodology
How we calculate. Step 1: nitrogen needed = (lawn sq ft ÷ 1,000) × target N rate (standard 1 lb N per 1,000 sq ft). Step 2: product needed = nitrogen needed ÷ N fraction on the bag (e.g. 24-6-6 = 0.24). University extensions cap annual nitrogen at 2 lbs per 1,000 sq ft.
Cross-checked. Our 1-lb-N rate and bag-math method match cooperative extension guidance; a soil test is the only way to know if you also need phosphorus or potassium.
Sources:
- NC State Extension — Caring for Your Lawns and the Environment (1 lb N per 1,000 sq ft; bag-rate table)
- University of Maine Extension — Fertilizing Lawns (max 2 lbs N per 1,000 sq ft per year)
Last updated: October 2026.
Frequently Asked Questions
Common questions about lawn fertilization and NPK ratios.
Related Calculators
🌾 Grass Seed Calculator 🌿 Sod Calculator 🌱 Topsoil Calculator ♻️ Compost Calculator 🍂 Mulch Calculator💡 Fertilizer Schedule
Spring: Light feeding — starter or balanced
Summer: Slow release only
Early Fall: Heavy feeding — high nitrogen
Late Fall: Winterizer — high potassium
Winter: No fertilizer