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Lawn Feed Calculator — How Much Lawn Feed Do I Need?
Calculate the right amount of lawn feed, weed and feed, or seasonal fertiliser for your lawn area. UK application rates.
Length of your lawn
Width of your lawn
Enter your supplier price for a cost estimate
Weight of small box (default 3.5kg)
Area covered by small box (default 100 m²)
Weight of large box (default 7kg)
Area covered by large box (default 200 m²)
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How We Calculate This
Our lawn feed calculator multiplies your lawn area by the standard application rate to work out how much product you need, then converts this to the number of boxes or bags required.
The formula
Lawn area = Length × Width
Product needed (g) = Area (m²) × Application rate (g/m²)
Boxes = Area ÷ Box coverage (rounded up)
Application rates
- Spring feed: ~35 g/m² (high nitrogen N:P:K)
- Summer feed: ~35 g/m² (balanced N:P:K)
- Autumn feed: ~35 g/m² (high potassium N:P:K)
- Weed & Feed: ~35 g/m² (combined herbicide + feed)
Standard box sizes
- Small box: 3.5 kg — covers approx. 100 m²
- Large box: 7 kg — covers approx. 200 m²
Always check the specific product instructions as rates and coverage may vary between manufacturers. Our calculator uses 35 g/m² — the most common UK branded rate (Westland SafeLawn, Miracle-Gro EverGreen Spring & Summer and Autumn all apply at 35 g/m² by hand or spreader). UK guidance gives a 25–35 g/m² range, so confirm against your product label before ordering.
Frequently Asked Questions
Most UK lawn feeds recommend an application rate of approximately 35 grams per square metre (35g/m²). This is equivalent to a small handful per square metre. A standard 3.5kg box covers about 100m², and a 7kg box covers about 200m². Always check the specific product instructions as rates can vary between brands. Starting a new lawn? See our Turf Calculator for turf quantities.
Feed your lawn three times per year for the best results. Apply spring feed (high nitrogen) in March to May for green-up and strong growth. Use summer feed in June to August to maintain health during hot weather. Apply autumn feed (high potassium) in September to November to build root strength and winter hardiness. Weed & Feed products are best applied April to September.
A lawn spreader gives much more even coverage and is strongly recommended for areas over 50m². Hand application tends to be uneven, leading to stripy results — dark green patches where too much was applied and pale patches where it was missed. If applying by hand, split the product into two halves and apply in perpendicular directions for more even coverage.
Yes, over-application (known as fertiliser burn or scorching) is a common mistake. It causes yellow or brown patches and can kill the grass. Always follow the recommended application rate of 35g/m². If you are unsure, it is better to apply slightly less than too much. Water well after application if no rain is forecast within 48 hours.
Ideally, apply lawn feed when rain is forecast within 24-48 hours, or water the lawn lightly after application. This helps the granules dissolve and reach the roots. Do not apply in drought conditions or when the grass is dormant. For weed & feed products, you need the leaves to be damp for the weed killer to stick — apply when dew is on the lawn.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.