Lawn Fertilizer N-P-K Calculator
Turn your target amount of actual nitrogen into fertilizer product to spread and bags to buy.
This is quantity math. The example nitrogen target is not a recommendation for your lawn.
Your fertilizer application
Fertilizer product needed
lb to spread
- Actual nitrogen required
- lb N
- Product application rate
- lb product / 1,000 sq ft
- Nitrogen supplied
- lb N
- Phosphate supplied
- lb P₂O₅
- Potash supplied
- lb K₂O
Application plan
Shopping list
- Exact bags required
- bags
- Whole bags to buy
- bags
- Product purchased
- lb
- Product left after this application
- lb
- Approximate one-bag coverage at entered nitrogen rate
- sq ft
Purchase and applied-product value
- Whole-bag purchase cost
- Purchase cost per 1,000 sq ft
- Approximate value of product applied
Purchase cost uses whole bags. Applied-product value is prorated; it is not the checkout amount.
Results are rounded for readability. Calculations use unrounded values. Coverage assumes even application at the entered rate; it is not label coverage.
What does N-P-K mean?
The bag numbers are percentages by weight: N is nitrogen, P is phosphate (P₂O₅), and K is potash (K₂O). These P and K numbers are not elemental phosphorus and potassium percentages. A 24-0-11 fertilizer contains approximately 24 lb nitrogen, 0 lb phosphate and 11 lb potash per 100 lb of product.
Why product rate differs by fertilizer
More concentrated nitrogen requires less fertilizer product for the same nitrogen target. To supply 1 lb N, a 10% N fertilizer needs 10 lb product; a 25% N fertilizer needs 4 lb product.
Fertilizer rate vs label rate
If your product label already tells you to apply a specific number of pounds of product per 1,000 sq ft, use the Lawn Granule Application Calculator instead. This N-P-K calculator is for applications planned around a target amount of actual nitrogen.
How it works
Nitrogen needed = lawn area ÷ 1,000 × target nitrogen rate. Fertilizer needed = nitrogen needed ÷ (N percentage ÷ 100). Nutrient amounts describe product actually applied, not all product purchased.
Calculate the amount — don't guess the agronomy
This calculator does not determine the correct nitrogen rate for your lawn. Needs depend on grass species, season, climate, soil conditions, soil test, irrigation, fertilizer formulation, local nutrient restrictions and product label instructions. Follow the label and applicable local requirements; do not exceed label directions.
Some areas restrict phosphorus-containing lawn fertilizers. Follow local requirements and the product label. Calculated phosphate contribution is not a recommendation to apply it.