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Generated on: July 20, 2026 at 09:33 PM

Fertilizer Application Calculator

Inputs

Area100 m²
Nitrogen rate5 g/m²
Nitrogen content26 %

This is an estimate based on the nitrogen content stated on the label and a target nitrogen rate. Always follow the product label for application rates and timing, and observe local regulations on fertilizer use, including setbacks near water bodies and seasonal application bans.

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Lifestyle

Fertilizer Application Calculator

Work out how much fertilizer product to apply to reach a target nitrogen rate over a given area, from the rate and the nitrogen content on the bag.

Inputs

≥ 0 m²
0.5 – 50 g/m²
%
1 – 100 %

Results

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Details

To apply 5 g/m² of nitrogen over 100 m² with a 26 % nitrogen fertilizer, spread about ... of product (a product rate of ...).

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Fertilizer Application

A fertilizer application rate is the weight of product spread over an area to deliver a target amount of actual nitrogen. Because a bag of fertilizer is only partly nitrogen, the product needed is more than the nitrogen figure itself, and this calculator converts a target nitrogen rate into the product weight to apply.

Product equals N rate divided by %N

A nitrogen rate is an amount of actual nitrogen per unit of area. The first number of the N-P-K analysis on the bag gives the nitrogen fraction of the product, so the product rate — the amount of product per unit of area — is the nitrogen rate divided by that fraction:

p=rn\begin{aligned} p &= \frac{r}{n} \end{aligned}

where rr is the nitrogen rate and nn is the nitrogen fraction. A leaner bag has a smaller nitrogen fraction, so more product is needed to deliver the same nitrogen.

Scaling by area

Multiplying the product rate by the total area gives the amount to apply:

W=p⋅A=rn⋅A\begin{aligned} W &= p \cdot A = \frac{r}{n} \cdot A \end{aligned}

where AA is the area. Enter the nitrogen rate in g/m² or lb/1000 ft²; the calculator reports the product weight in kilograms or pounds to match.

Worked example

Consider a 100 m² lawn fed at 5 g of nitrogen per square metre with a 26-0-0 fertilizer (26% nitrogen):

p=50.26≈19.2 g per m2W=19.2⋅100≈1920 g=1.9 kg\begin{aligned} p &= \frac{5}{0.26} \approx 19.2 \ \text{g per m}^2 \\ W &= 19.2 \cdot 100 \approx 1920 \ \text{g} = 1.9 \ \text{kg} \end{aligned}

So about 1.9 kg of product covers the lawn at the target rate. Always follow the application rate on the product label and observe local regulations on fertilizer use, particularly setbacks near water bodies.

Consider a 1000 sq ft lawn fed at 1 lb of nitrogen per 1000 sq ft with a 26-0-0 fertilizer (26% nitrogen):

p=1.00.26=3.85 lb per 1000 sq ftW=3.85⋅10001000≈3.85 lb\begin{aligned} p &= \frac{1.0}{0.26} = 3.85 \ \text{lb per 1000 sq ft} \\ W &= 3.85 \cdot \frac{1000}{1000} \approx 3.85 \ \text{lb} \end{aligned}

So about 3.85 lb of product covers the lawn at the target rate. Always follow the application rate on the product label and observe local regulations on fertilizer use, particularly setbacks near water bodies.

To work out how much seed the same lawn needs, see Grass Seed Calculator.

Frequently Asked Questions (FAQ)

How much fertilizer do I need?

The amount depends on the target nitrogen rate, the area, and the nitrogen content of the product. Divide the rate by the nitrogen fraction to get the product rate, then scale by the area. As a worked example, applying 5 g of nitrogen per m² over 100 m² with a 26-0-0 fertilizer (26% nitrogen) needs about 19 g of product per m², or roughly 1.9 kg of product in total.

The amount depends on the target nitrogen rate, the area, and the nitrogen content of the product. Divide the rate by the nitrogen fraction to get the product rate, then scale by the area. As a worked example, applying 1 lb of nitrogen per 1000 sq ft over 1000 sq ft with a 26-0-0 fertilizer (26% nitrogen) needs about 3.85 lb of product per 1000 sq ft, or roughly 3.85 lb of product in total.

What is a nitrogen rate?

A nitrogen rate is the amount of actual nitrogen applied per unit of area. A maintenance feeding is often around 5 g of nitrogen per square metre per application, with annual totals split across several feedings. Rates depend on the grass or crop, the season, and the product, so the figure recommended for the specific grass, crop, and product should be followed.

A nitrogen rate is the amount of actual nitrogen applied per unit of area, quoted in pounds of nitrogen per 1000 square feet in standard turf and agronomy practice. A maintenance feeding is often around 1 lb of nitrogen per 1000 sq ft per application, with annual totals split across several feedings. Rates depend on the grass or crop, the season, and the product, so the figure recommended for the specific grass, crop, and product should be followed.

How do I read the N-P-K numbers on the bag?

The three numbers on a fertilizer label are the percentages by weight of nitrogen (N), phosphorus pentoxide (P₂O₅), and potassium oxide (K₂O). A 26-0-0 bag is 26% nitrogen by weight, so 1 kg of it contains 260 g of actual nitrogen. This calculator uses only the first number, the nitrogen percentage, to convert a target nitrogen rate into a product quantity.

The three numbers on a fertilizer label are the percentages by weight of nitrogen (N), phosphorus pentoxide (P₂O₅), and potassium oxide (K₂O). A 26-0-0 bag is 26% nitrogen by weight, so 100 lb of it contains 26 lb of actual nitrogen. This calculator uses only the first number, the nitrogen percentage, to convert a target nitrogen rate into a product quantity.

Disclaimer

This is an estimate based on the nitrogen content stated on the label and a target nitrogen rate. Always follow the product label for application rates and timing, and observe local regulations on fertilizer use, including setbacks near water bodies and seasonal application bans.

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