Fertilizer Ratio Calculator

Convert between N-P-K ratios, calculate application rates per square foot, and compare fertilizer products.

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How It Works

The three numbers on a fertilizer label represent the N-P-K ratio—the percentage by weight of three key nutrients:

• N (Nitrogen) – Promotes leafy green growth
• P (Phosphorus) – Supports root development and flowering
• K (Potassium) – Strengthens overall plant health and disease resistance

Reading the Label

A bag labeled 10-10-10 contains 10% nitrogen, 10% phosphorus (as P&sub2;O&sub5;), and 10% potassium (as K&sub2;O) by weight. A 50 lb bag of 10-10-10 contains 5 lb of each nutrient.

Application Rate

If you need 1 lb of nitrogen per 1,000 ft² and your fertilizer is 10-10-10:

For a 5,000 ft² lawn, that would be 50 lb of fertilizer total.

Comparing Products

To compare value between products, the calculator computes the cost per pound of actual nutrient. A cheaper bag isn’t always a better deal if it has a lower nutrient concentration.

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Common Fertilizer Reference

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