Lawn Fertilizer Calculator
Work out how many bags of fertilizer your lawn needs — based on the coverage on your bag.
Last reviewed 2026-06-06
Fertilizer bags are sold by the area they cover — “feeds 5,000 sq ft” — not by your lawn’s size, so a quick calculation tells you how many bags to buy. Get it wrong and you either run short mid-lawn (leaving stripes) or over-apply and scorch the grass.
Enter your lawn dimensions and the coverage printed on the bag, and we tell you how many bags to buy and how much area you will actually cover.
How to use the Lawn Fertilizer Calculator
- Measure the length and width of the lawn (split odd shapes into rectangles).
- Find the “covers X sq ft” figure on your fertilizer bag and enter it.
- Read off the number of bags to buy.
- Apply with a spreader at the labelled rate — never more.
Frequently asked questions
How much fertilizer do I need for my lawn?
Divide your lawn’s area by the coverage printed on the bag (for example 5,000 sq ft per bag) and round up. A 2,000 sq ft lawn needs one 5,000 sq ft bag; a 12,000 sq ft lawn needs three.
How often should I fertilize?
Most lawns benefit from 2–4 feedings per growing season, spaced 6–8 weeks apart, following the product’s schedule. Cool-season grasses are usually fed in spring and autumn; warm-season grasses through summer.
Can I use too much fertilizer?
Yes — over-application burns the grass (yellow or brown streaks) and can run off into waterways. Always apply at or below the labelled rate, and use a spreader for an even spread rather than dumping by hand.
Should I water after fertilizing?
Usually yes — watering in helps granular fertilizer reach the soil and reduces the risk of burn, unless it is a “weed and feed” that needs to stay on the leaf first. Follow the bag’s instructions.