How Much Fertilizer Do I Need?

How fertilizer is actually measured

Lawns are fed by pounds of nitrogen per 1,000 sq ft, not by pounds of bag. Two products can both say "lawn fertilizer" and contain very different amounts of nitrogen, so you have to translate your lawn's nitrogen need into pounds of that specific bag.

The manual way

1. Start with your square footage. This is the number every dose is based on (how to measure your yard).
2. Pick a nitrogen rate. Most feedings target 0.5 to 1 lb of nitrogen per 1,000 sq ft. A safe all-purpose number is 0.75.
3. Read the first NPK number. The three numbers on the bag are nitrogen, phosphorus, and potassium. The first is the percent nitrogen, so a 32-0-6 bag is 32% nitrogen.
4. Run the formula. Multiply your nitrogen rate by your square footage, divide by 1,000, then divide by the nitrogen percent written as a decimal.

Worked example: 0.75 lb N, a 5,000 sq ft lawn, and a 32-0-6 bag. First, 0.75 x 5,000 / 1,000 = 3.75 lbs of nitrogen needed. Divide that by 0.32 and you get about 11.7 lbs of fertilizer. Spread it in two passes, half north-south and half east-west, then water it in.

The easy way with SimpleLawn

The formula is not hard, but running it every time you are standing in the store gets tedious. In SimpleLawn you enter your lawn size and the bag's NPK, and it returns the exact pounds to buy plus how to set your spreader.

The bigger win is measuring only once. When you map your lawn in SimpleLawn (how to measure your yard), it saves the square footage of every zone. So the next time you reach for fertilizer, the size is already filled in. You pick the bag and get the pounds instantly, with no tape measure and nothing to retype. Measure once, and every dose after that takes seconds.

Want to try it right now? Open the free lawn treatment calculator, no download needed.