Lawn Feed Calculator
Calculate how much lawn feed, weed killer or grass seed you need for your lawn. Enter dimensions or total area to get quantities, packs and cost.
Using 35 default
Total Cost
£12.00
Application Tip
Always follow product instructions for best results. Apply spring feed in March-April, autumn feed in September-October.
Grams Per Square Metre, Done Properly
Lawn feed is sold in bold packaging that hides the only number that actually matters: the application rate in grams per square metre. Spring and autumn feeds typically apply at 35 g/m². Weed and feed sits closer to 30 g/m². Moss killer goes on lighter at 20 g/m². Go above the rate and you scorch the lawn into yellow stripes that take months to recover.
The calculator's default is a 10m by 8m lawn (80 m²) treated with spring feed at 35 g/m². That works out to 2.8 kg of product. At 200 m² coverage per pack, one pack does the job, costing £12 at the default price. A typical UK back garden lawn (around 50 m²) needs about 1.75 kg of feed per application, so a single 200 m² pack covers two or three applications across the year.
Timing and Application Mistakes
Spring feed goes down March to April once the grass is actively growing and overnight frosts have eased. Autumn feed (lower in nitrogen, higher in potassium) goes down September to October to harden the lawn before winter. Apply on a still, dry day; rain within 48 hours either washes weed killer off the leaf or burns the lawn if a granule clumps in one spot. A drop spreader gives a far more even result than throwing handfuls.
Common errors: doubling back over the same strip and applying twice the rate, not watering in granular feed within a week, and trying to feed a stressed lawn during a heatwave. If the lawn is yellow and crisp, water it back into life first; feeding adds insult to injury. For seeding or repair work after weed control, wait at least four weeks for the chemistry to clear.
Frequently Asked Questions
How much lawn feed do I need for my lawn?
Multiply your lawn area in square metres by the application rate (typically 35 g/m² for standard spring or autumn feed). A 50 m² lawn needs 1.75 kg per application. Always check the back of your specific product, since organic and slow-release feeds use different rates.
When is the best time to apply lawn feed?
Spring feed: March to April, once grass is growing and frosts have passed. Autumn feed: September to October, before the first frosts. Avoid feeding during summer drought or in waterlogged winter conditions; both stress the grass and waste the product.
Can I use weed and feed and grass seed together?
No. The weed killer in weed and feed prevents new seedlings from establishing. Wait at least four weeks (six is safer) after applying weed and feed before overseeding. Plain grass seed and a separate spring feed used in tandem is the cleaner way to thicken up a lawn.
What happens if I apply too much lawn feed?
Over-application scorches the lawn within days, leaving yellow or brown stripes wherever the granules concentrated. Heavy rain after application carries excess nitrogen into drains and waterways. If you spot scorch, soak the area heavily for a week to flush the salts and let the grass recover; reseed bare patches in autumn.
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