Why a lawn feed calculator should not choose your fertiliser rate
Different lawn products contain different nutrients, release patterns and additional active ingredients. RHS advice is therefore straightforward: if a lawn needs feeding, use the product at the manufacturer's recommended rate. The calculator's role is only to turn that rate into a quantity for your measured area.
A current Miracle-Gro Complete 4 in 1 product, for example, publishes a maximum individual dose of 35g/m². That is useful evidence of how one product is labelled; it is not a universal rate for every feed. Liquid lawn products use different mL-per-area instructions again.
Three different questions, three different calculations
5kg at 35g/m²
5,000g ÷ 35g/m² = 142.86m². That is theoretical pack coverage before practical variation from spreading.
Granular feed: keep the units visible
The calculator accepts g/m², kg per 100m² or g per 100m² and normalises the value internally. This prevents a common unit error. For example, 3.5kg per 100m² is exactly 35g/m²; 35g per 100m² would be only 0.35g/m².
Liquid feed needs product-specific dilution
Some liquid lawn products are labelled with an amount of concentrate per treated area and a separate dilution for a watering can or sprayer. Those details can differ even between products from the same manufacturer. The calculator therefore totals concentrate quantity only from the label's area dose; it does not invent a watering-can dilution or pressure-sprayer setting.
Multiple applications: total purchasing, not a feeding schedule
If the product label or your chosen lawn-care programme calls for more than one application, the tool can total the product across the number you enter. That feature does not recommend how often to feed. RHS notes that many lawns grow well without feeding and advises using fertiliser only when needed and at the appropriate product rate.
Avoid the expensive mistake: more feed is not automatically better
RHS identifies regular brown stripes or patches after lawn feeding as a possible sign of fertiliser overdose and advises using the correct dose evenly. Mechanical spreaders should be calibrated for the product being applied. Do not increase the calculator's rate to chase a faster result.
Worked lawn-feed examples
3,500g = 3.5kg per application. One 5kg pack is enough for that single application.
7,500g = 7.5kg. With 5kg packs, round up to 2 whole packs.
5,000 ÷ 35 = about 142.86m² theoretical coverage.
100m² at 35g/m² needs 3.5kg each time, or 10.5kg total; that would require 3 whole 5kg packs.
Lawn feed is not grass seed or topdressing
The Grass Seed Calculator calculates seed from a sowing rate. The Lawn Topdressing Calculator calculates a physical dressing volume from millimetres of depth. This page is specifically for fertiliser/feed quantity from a product's stated application rate.
For calculation conventions and rounding, see How our calculations work.