🌱 Garden & farm

Fertilizer Application Rate

Work out how much fertilizer delivers a target nitrogen rate over an area. Enter the N-P-K analysis, bag weight and target, then press Convert.

Written and reviewed by SM Arijul Islam · Last reviewed 27 October 2026 · Editorial standards · Report an error

About the Fertilizer Application Rate

A fertilizer label such as 10-10-10 means 10% nitrogen, 10% available phosphate (P₂O₅) and 10% soluble potash (K₂O) by weight. To apply 1 lb of actual nitrogen per 1,000 sq ft with a 10% product, you need 10 lb of product per 1,000 sq ft — the other 9 lb is carrier and other nutrients.

This calculator solves for product weight, not nutrient weight. It also reports how much P and K those bags deliver, which is often more than a soil test calls for. Apply nitrogen to the rate your soil test or crop guide recommends, and split applications on sandy or high-rainfall ground.

How the calculation works

Product (lb) = target N (lb/1,000 ft²) × area (ft²) ÷ 1,000 ÷ (N% ÷ 100).
Bags = product weight ÷ bag weight.
P₂O₅ applied = product × P% ÷ 100.
K₂O applied = product × K% ÷ 100.

Reference values

How much product a target nitrogen rate requires
Product	Product for 1 lb N / 1,000 ft²	N per 10 lb product
46-0-0 (urea)	2.17 lb	4.6 lb
34-0-0 (ammonium nitrate)	2.94 lb	3.4 lb
21-0-0 (ammonium sulfate)	4.76 lb	2.1 lb
10-10-10	10 lb	1.0 lb
20-10-10	5 lb	2.0 lb

Worked example: 5,000 sq ft at 1 lb N

To apply 1 lb of nitrogen per 1,000 sq ft over 5,000 sq ft, you need 5 lb of nitrogen. With a 10-10-10 product, that is 50 lb of product. With 46-0-0 urea, it is 10.9 lb. The 10-10-10 also delivers 5 lb of P₂O₅ and 5 lb of K₂O—check whether the soil test actually calls for them.

Water the lawn after applying granular fertilizer unless the label says otherwise. Water moves the nutrients into the root zone and reduces the risk of burn. Avoid applying before heavy rain, which can wash the product into drains and waterways.

Frequently asked questions

Does N-P-K mean nitrogen, phosphorus and potassium?

The N is nitrogen. The P number is actually P₂O₅ (phosphate) and the K number is K₂O (potash), expressed as if they were the oxides. Elemental P and K are lower.

Can I apply all the nitrogen at once?

For lawns, split it across the growing season. For row crops, follow the crop guide; a single large dose is easily leached or volatilised.

Why does my 10-10-10 deliver so much phosphorus?

Because the ratio is fixed. If soil P is already high, choose a product with a lower P number rather than applying unnecessary phosphate.

Should I water after applying fertilizer?

Yes for most granular products, unless the label says otherwise. Water moves the nutrients into the root zone and reduces the risk of burn; avoid applying before heavy rain.