Garden Fertilizer Calculator
Matching Fertilizer Bag to Bed Size
Fertilizer labels advertise an N-P-K percentage, not a dose — a bag marked "10-10-10" and one marked "46-0-0" deliver wildly different amounts of nitrogen per pound. Applying by instinct risks under-feeding a bed or, worse, burning roots with excess nitrogen. This calculator converts a target nitrogen application rate and the fertilizer's labeled nitrogen percentage into the actual weight of product to spread.
The Formula
Desired N rate is expressed in pounds of actual nitrogen per 1,000 square feet — a standard unit in lawn and garden fertilizer guidance — and N% is the first number in the fertilizer's N-P-K ratio on the label.
How Much Product for 1,000 sq ft?
At a common target rate of 1 lb of actual nitrogen per 1,000 sq ft, the amount of product needed depends entirely on how concentrated the fertilizer is:
| Fertilizer | N-P-K (typical) | Product Needed |
|---|---|---|
| Urea | 46-0-0 | 2.17 lbs |
| Ammonium sulfate | 21-0-0 | 4.76 lbs |
| Balanced all-purpose | 10-10-10 | 10.0 lbs |
| Blood meal | 12-0-0 | 8.33 lbs |
N-P-K figures are typical label values — always use the percentage printed on your specific product, since formulations vary by manufacturer.
Where This Calculation Matters
- Vegetable beds at planting — matching nitrogen rate to crop needs (heavy feeders like corn and tomatoes vs. light feeders like beans) without over-applying.
- Lawn feeding programs — most turf guidance specifies an annual or per-application nitrogen budget in lbs per 1,000 sq ft, exactly the unit this formula solves for.
- Switching fertilizer brands — converting a rate you've dialed in with one product to the correct dose of a different-strength fertilizer.
How to Use This Calculator
- Enter the area to be fertilized in square feet.
- Enter the fertilizer's nitrogen content as a percentage — the first number in its N-P-K ratio (e.g. enter 10 for a 10-10-10 product).
- Enter the desired nitrogen application rate in lbs per 1,000 sq ft (defaults to 1, a common general-purpose rate).
- Select Calculate to get the exact weight of fertilizer product to apply.
Related Calculations
Once beds are fertilized, dial in irrigation with the Garden Watering Schedule Calculator, or size new growing medium with the Garden Soil Calculator.