For a granular lawn feed with a rate given in grams per square metre, multiply the area you are treating by the rate on the product label. Divide the result by 1,000 to convert grams to kilograms.
Lawn area (m²) × label rate (g/m²) ÷ 1,000 = kilograms for one application.
Use the actual rate for your product and the part of the lawn you intend to treat. The numbers in the example below are hypothetical; they are not a recommendation for every fertiliser. Liquid feeds may use different units and dilution directions, so follow their labels instead of using this formula unchanged.
Measure the grass area
For a rectangle, multiply the length by the width. If a lawn is 8 metres long and 5 metres wide, its area is 40m². For an irregular lawn, divide it into simpler sections, calculate each area and add them. Leave out paths, beds and other surfaces you will not treat.
If you are treating only part of a lawn, measure that part. For separate lawns receiving the same feed at the same rate, add their treatment areas before calculating the quantity.
A worked example
Imagine a 40m² lawn and a granular fertiliser whose label says 30g/m². The calculation is 40 × 30 = 1,200g. Divide by 1,000: you would need 1.2kg for one application.
If your label gives a different rate, replace 30 with that figure. Check whether the stated pack coverage refers to one application, and choose enough product for your measured area. Do not increase the dose to use up a partly full bag.
Measure and apply it evenly
Weigh out the calculated amount before applying. A suitable spreader can help cover the area evenly, but settings depend on the product and equipment; follow the manufacturer’s calibration instructions. See how to apply lawn fertiliser evenly for the spreading steps and what to do with spills.
Check the label for suitable weather, watering, storage, safety and the interval before another application. The RHS notes that overuse and incorrect application can cause pollution. Feeding is not always necessary: our seasonal feeding guide explains when to consider it.
Can I use this calculation for Spritely feeds?
Our proposed Spring & Summer Lawn Feed and Autumn Lawn Feed are in development and out of stock. Their application rates and pack details have not yet been confirmed. Use the final product label when those details are available.