Turn a nitrogen target into pounds of the actual bag in your hands — the N-P-K percentage math every extension service teaches, done for you.
What the three numbers mean
The 10-10-10 on a fertilizer bag is percentages by weight: nitrogen, phosphate and potash. Lawn and garden guidance is written in pounds of nitrogen per 1,000 square feet — commonly around 1 lb N per application for lawns — so the job is always the same conversion: divide the nitrogen target by the bag’s %N to get pounds of product. Enter the area, the target and the bag’s first number, and this calculator does it.
How to use it
- Enter the area to feed in square feet.
- Enter the nitrogen target — 1 lb N / 1,000 sq ft is the common lawn application.
- Enter the bag’s first number (%N) and read the product weight.
The formula
A worked example
A 5,000 sq ft lawn at 1 lb N per 1,000 needs 5 lb of actual nitrogen — on a 10-10-10 bag that’s 50 lb of product (10 per 1,000). The same target from a 29-0-4 turf fertilizer needs only 17 lb, which is the entire reason two bags of very different weights can be “the same application”. More is not better: doubling nitrogen burns lawns and feeds runoff, and splitting the year’s total across several applications beats one heavy one.