Fertilizer Calculator: Pounds of N-P-K
This fertilizer calculator tells you how much product to spread on a lawn or garden bed. Enter the area in square feet, the three N-P-K numbers on the bag, the nutrient you are targeting and the rate in pounds per 1,000 square feet. For lawns that is usually nitrogen at 0.5 to 1 pound per 1,000 sq ft per feeding. It returns pounds of product per 1,000 sq ft, total pounds and bags for your area, and how much nitrogen, phosphate and potash you will apply. This helps avoid overfeeding, which burns grass and washes nutrients into waterways.
Fertilizer Calculator
How much fertilizer to spread for a target pound of nitrogen per 1,000 sq ft.
How to use the Fertilizer Calculator
- Enter the lawn or bed area in square feet.
- Enter the N-P-K numbers from the bag, such as 29-0-4.
- Choose the nutrient and target rate per 1,000 sq ft.
- Enter the bag size and read the pounds and bags needed.
Fertilizer formula
Product per 1,000 sq ft = target rate ÷ (nutrient % ÷ 100). Total = per 1,000 × area ÷ 1,000. Bags = total ÷ bag size, rounded up.
Features
- Works with any N-P-K grade
- Target nitrogen, phosphate or potash
- Pounds per 1,000 sq ft and total
- Bags needed
- Nutrients applied
- US units (lb, sq ft)
Frequently asked questions
How much fertilizer do I need per 1,000 square feet?
Divide the target nutrient rate by the nutrient percent. For 1 lb of nitrogen with 29-0-4 fertilizer: 1 ÷ 0.29 = 3.45 lb of product per 1,000 sq ft.
What do the three numbers on a fertilizer bag mean?
They are the percent by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). A 50 lb bag of 10-10-10 has 5 lb of each.
How much nitrogen does a lawn need?
Most US lawns need about 0.5 to 1 lb of nitrogen per 1,000 sq ft per feeding and about 2 to 4 lb per year, depending on grass type.
Can I put down too much fertilizer?
Yes. Too much nitrogen can burn grass and runs off into streams. Follow the bag label and local rules, some of which limit phosphorus.
How do I measure my lawn area?
Multiply length by width in feet for each rectangle and add them up, or use the square footage calculator linked below.