Fertilizer Cost Calculator: Price per Pound of Nitrogen

Fertilizer is priced by the bag and used by the pound of nitrogen, and those two things have almost nothing to do with each other. A bag that costs less can easily be the more expensive fertilizer, because most of what you’re carrying to the truck is filler.

This works out what each bag actually costs for the nutrient you’re buying. Enter the weight, the first of the three numbers on the front, and the price. It’ll tell you the cost per pound of nitrogen, how much nitrogen is in the bag, and how much lawn it covers — for two bags at once, so you can settle it standing in the aisle.

How It Works

Three numbers on the front of a fertilizer bag are percentages by weight. The first is nitrogen. So a 50-pound bag reading 22-0-12 holds 22% of 50 pounds — eleven pounds of actual nitrogen. Divide the price by that figure and you have the number that lets you compare any two bags on the shelf, regardless of size or brand.

The coverage figure assumes one pound of nitrogen per 1,000 square feet, which is the standard rate for a single application on cool-season grass. Eleven pounds of nitrogen covers 11,000 square feet at that rate. If you know your lawn’s square footage, that tells you how many applications a bag holds.

What This Doesn’t Tell You

Cost per pound of nitrogen is the right way to compare price. It is not the whole decision.

Turn the bag over and find the guaranteed analysis. Nitrogen derived from polymer-coated or sulfur-coated urea releases over eight to twelve weeks; nitrogen from ammonium nitrate or plain urea is available the moment it gets wet. The slow-release version is easier on the lawn, much harder to burn with, and genuinely worth paying more per pound for. Two bags with identical front numbers can be different products.

The calculator also ignores phosphorus and potassium, which matter but aren’t usually what drives the price difference between two bags on the same shelf.

The Short Version

Small bags of low-analysis fertilizer are the most reliably bad value in the lawn aisle. They’re light enough to carry with one hand, cheap enough on the shelf tag, and frequently cost four or five times as much per pound of nitrogen as the fifty-pound bag two spots over. That’s the gap this is built to show you.

For the full explanation of the label — what the middle number means, why it’s usually zero in Wisconsin, and the line on the back that matters more than the numbers on the front — read what the numbers on a fertilizer bag actually mean.