Fertiliser Rate Calculator

Calculate the total fertiliser product needed for a paddock based on area and application rate.

Total fertiliser needed = paddock area × application rate. A 50 ha paddock at 100 kg/ha requires 5,000 kg (5 t) of product.

Calculator

Paddock area (ha)Total area to be fertilised.Application rate (kg/ha)Product rate from your agronomist recommendation or the product label.

Total product required

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How it works

Multiply the paddock area in hectares by the product application rate in kg/ha. The result is the gross quantity to order before accounting for bag wastage, GPS overlap, or headland areas.

Worked example

50 ha × 100 kg/ha = 5,000 kg. At a standard 25 kg bag that is 200 bags — or 5 tonne in bulk.

Assumptions & limitations

The application rate entered is the product rate, not a pure-nutrient rate. If your recommendation is in kg of nutrient per hectare, divide by the product's nutrient concentration (as a decimal) before entering here. For example, urea is 46% N: 30 kg N/ha ÷ 0.46 = 65 kg urea/ha. GPS overlap and headland turns typically add 3–8% — round up when ordering.

Frequently asked questions

What is the difference between product rate and nutrient rate?

A nutrient rate (e.g. 30 kg N/ha) tells you how much pure nitrogen to apply. A product rate tells you how many kilograms of the actual fertiliser bag to spread. Convert by dividing: product rate = nutrient rate ÷ (nutrient concentration ÷ 100). Urea is 46% N, so 30 kg N/ha requires 65 kg urea/ha.

How do I account for spreader overlap and headland turns?

Add 5–10% to the calculated total to cover headland turns, tram-line overlap, and loading losses. For a 5,000 kg requirement, budget 5,250–5,500 kg when ordering.

How many bags do I need?

Divide the total by your bag size. For 5,000 kg in 25 kg bags: 5,000 ÷ 25 = 200 bags. Most suppliers sell in full pallets — a standard pallet holds 40 × 25 kg bags (1,000 kg), so 5 pallets.

What application rate should I use?

Use the rate from a soil test recommendation or agronomist prescription. Applying fertiliser without a soil test risks under- or over-fertilising — both cost money and can harm crop production or the environment.

Last updated 22 June 2026

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