To work out how much fertilizer to apply, multiply your target nitrogen rate (usually 1 pound of nitrogen per 1,000 square feet) by your lawn area, then divide by the fertilizer’s nitrogen percentage, which is the first number on the bag. For a 5,000 sq ft lawn and a 24-0-4 fertilizer, that is about 20.8 pounds of product. The calculator below does the math for you.
Key Takeaways
- Pounds of fertilizer = (target N rate × lawn sq ft ÷ 1,000) ÷ (nitrogen % ÷ 100).
- The standard rate is 1 lb of nitrogen per 1,000 sq ft per application; use 0.5 for a gentle feed.
- The first NPK number on the bag is the nitrogen percentage you plug in.
- Most lawns want 2 to 4 lbs of nitrogen per 1,000 sq ft per year, split across the growing season.
- Never exceed 1 lb of quick-release nitrogen in a single application, or you risk burning the lawn.
Quick-release nitrogen: stay at or below 1 lb per 1,000 sq ft per application. Slow-release products can go a little higher, so always follow the bag’s label.
How to read the NPK numbers
Every fertilizer bag shows three numbers, for example 24-0-4. They are the percentages by weight of nitrogen (N), phosphorus (P), and potassium (K). For this calculator you only need the first number, the nitrogen percentage, because nitrogen drives green growth and is what you dose by. A 24-0-4 bag is 24% nitrogen, so a 40 lb bag contains 9.6 lbs of actual nitrogen.
How much nitrogen does your lawn need?
Apply about 1 pound of nitrogen per 1,000 square feet per feeding, and aim for a yearly total based on your grass type. Warm-season grasses like Bermuda are heavier feeders than cool-season grasses.
| Grass type | Nitrogen per year (per 1,000 sq ft) |
|---|---|
| Bermuda | 4 to 6 lbs |
| St. Augustine / Zoysia | 2 to 4 lbs |
| Tall fescue | 2 to 4 lbs |
| Kentucky bluegrass | 2 to 4 lbs |
The fertilizer formula, worked through
Say you have a 5,000 sq ft lawn, a 24% nitrogen fertilizer, and you want the standard 1 lb of nitrogen per 1,000 sq ft.
- Nitrogen needed: 1 × (5,000 ÷ 1,000) = 5 lbs of nitrogen.
- Fertilizer needed: 5 ÷ 0.24 = about 20.8 lbs of product.
- Per 1,000 sq ft: 20.8 ÷ 5 = about 4.2 lbs of product.
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Feed when your grass is actively growing. Warm-season lawns are fed from late spring through summer; cool-season lawns are fed mainly in early fall and spring. Stop nitrogen 6 to 8 weeks before your first frost so you are not pushing tender growth into dormancy. Water lightly after applying granular fertilizer to move it off the blades and into the soil.
Frequently Asked Questions
How much fertilizer do I need for 5,000 square feet?
For 5,000 sq ft at the standard 1 lb of nitrogen per 1,000 sq ft, you need 5 lbs of actual nitrogen. With a 24% nitrogen fertilizer that is about 20.8 lbs of product, or roughly 4.2 lbs per 1,000 sq ft.
Which NPK number do I use to calculate fertilizer?
Use the first number, the nitrogen percentage. Lawns are dosed by nitrogen, so divide the nitrogen you need by that percentage (as a decimal) to get the pounds of product. Phosphorus and potassium are not used in this calculation.
Can you put down too much fertilizer?
Yes. More than about 1 lb of quick-release nitrogen per 1,000 sq ft in one application can burn the grass, leaving yellow or brown streaks. Stay at or below that rate, spread evenly, and water it in. Slow-release products are more forgiving.
How often should I fertilize my lawn?
Every 4 to 6 weeks during the growing season, up to your grass type’s yearly total. Bermuda wants 4 to 6 lbs of nitrogen per 1,000 sq ft a year; most other lawns want 2 to 4. Always feed when the grass is actively growing.
Get a free personalised lawn care plan with a feeding schedule for your grass, and see our guides to the best fertilizer for Bermuda grass and your grass type.
