How to Read a Fertilizer Label (N-P-K Explained)
Those three numbers on every fertilizer bag tell you exactly what is inside. Learn what N-P-K means, how to turn a nitrogen goal into pounds of product, and which other label details are worth checking.
By the CalcAndPlan Editorial Team · Published · 3 min read
In this article
The three numbers
The guaranteed analysis on a fertilizer bag is written as three numbers, such as 24-0-6. They are the percentages by weight of nitrogen (N), phosphate (P₂O₅), and potash (K₂O), always in that order.
A 50 lb bag of 24-0-6 contains 12 lb of nitrogen (24% of 50), no phosphate, and 3 lb of potash. The rest is other nutrients, filler, and coating that help the product spread evenly.
What each nutrient does
Nitrogen drives leafy, green growth, which is why lawn fertilizers usually have the highest first number. Phosphorus supports root development and is important when establishing new plants. Potassium helps plants handle stress such as drought and temperature swings.
Many areas restrict phosphorus in lawn fertilizer because runoff can harm lakes and streams, which is why many lawn products show a zero in the middle position. A soil test is the best way to know whether your soil actually needs phosphorus.
Run your numbersLawn Fertilizer CalculatorTurning a nitrogen goal into pounds of product
Lawn recommendations are usually given in pounds of actual nitrogen per 1,000 square feet. To find how much product delivers that, divide the nitrogen target by the nitrogen percentage as a decimal. For example, half a pound of nitrogen from a 25% product needs 0.5 ÷ 0.25 = 2 lb of product per 1,000 square feet.
Then multiply by your lawn area in thousands of square feet. The Lawn Fertilizer Calculator does both steps and tells you how many bags to buy.
Other label details worth reading
Look for the amount of slow-release or slowly available nitrogen. Slow-release products feed the lawn gradually, while quick-release products green up faster but can burn grass if over-applied.
The label also lists spreader settings, application timing, and any restrictions. Those directions are part of using the product correctly and override general advice, including anything you read online.
Granular versus liquid
Granular fertilizers are spread with a broadcast or drop spreader and are the most common choice for lawns. Liquid fertilizers are mixed with water and applied with a sprayer or hose-end applicator; they act quickly but may need more frequent application.
The label math is the same either way: the nitrogen percentage tells you how much product delivers the nitrogen you want. For liquids, labels often give the rate in fluid ounces per 1,000 square feet instead.
Calibrating your spreader
Spreader settings printed on the bag are starting points. To check yours, measure out a small area — say 100 square feet — weigh a known amount of product, spread it, and see how much is left. Adjust the setting until the amount used matches the rate you calculated.
Calibration takes a few minutes and prevents both wasted product and burned stripes in the lawn.
Worked example: feeding a 6,000 sq ft lawn
- Nitrogen target: 0.75 lb per 1,000 sq ft (from the label’s recommendation)
- Product: 30-0-4, so 30% nitrogen
- Product per 1,000 sq ft: 0.75 ÷ 0.30 = 2.5 lb
- Whole lawn: 6 × 2.5 = 15 lb
Spread about 15 pounds of product — one 15 lb bag would cover it exactly, so a slightly larger bag avoids running short.
Helpful tips
Pro tips
- Sweep fertilizer granules off driveways and sidewalks back onto the lawn so they don’t wash into storm drains.
- Split the product into two half-rate passes at right angles for more even coverage.
- Store bags sealed and off the floor in a dry place.
Frequently asked questions
Is a higher first number always better?
No. A higher nitrogen percentage just means less product per application. What matters is applying the right amount of nitrogen for your lawn and season.
What does 10-10-10 mean?
It’s a balanced fertilizer with 10% each of nitrogen, phosphate, and potash. It’s more common for gardens than for established lawns.
The bottom line
Read the three numbers as percentages, convert your nitrogen goal into pounds of product, and follow the label’s directions and local rules. A few minutes with the label saves money and protects both the lawn and nearby water.
Further reading
General information for planning. Conditions vary by region, site, and product — check product labels and local guidance.