Free tool

Fertilizer Calculator

Enter your lawn size and the fertilizer's N-P-K numbers to find out exactly how many pounds of product to apply — no more guessing at the spreader setting.

Lawn area

sq ft

Target nitrogen rate

lb N / 1,000 sq ft

0.5–1 lb per application is typicalFertilizer's N%

First number on the bag, e.g. 10 in 10-10-10

Fertilizer needed

50.0 lb

≈ 40 lb bags

1.25

Actual nitrogen applied

5.00 lb N

How this is calculated

Fertilizer needed (lb) = (area ÷ 1,000) × target lb of nitrogen per 1,000 sq ft ÷ (fertilizer's nitrogen percentage ÷ 100).

A rate of 0.5–1 lb of actual nitrogen per 1,000 sq ft per application is standard extension guidance for most cool- and warm-season lawns — check your fertilizer guide for grass-specific timing.