Grass Seed Calculator
How much grass seed a lawn needs, and how many bags, from the area and the seeding rate printed on your seed bag, for a new lawn or for overseeding an existing one.
Result…
How it's calculated
Seed (kg) = rate (g/m²) × area (m²) ÷ 1000 Seed (lb) = rate (lb per 1,000 ft²) × area (ft²) ÷ 1000 With extra = seed × (1 + extra % ÷ 100) · bags = seed ÷ bag size, rounded up 1 lb per 1,000 ft² = 453.59237 g ÷ 92.90304 m² = 4.8824 g/m²
Multiplies the lawn area by the seeding rate to get the weight of seed, adds an optional allowance for waste, and rounds up to whole bags. Seed bags usually print two rates: a heavier one for a new lawn on bare soil and a lighter one for overseeding, which thickens an existing lawn. Choose which one you are doing and enter that rate from your bag: rates vary widely between grass species and mixes, so this calculator does not suggest one. Metric rates are in grams per square metre and imperial rates in pounds per 1,000 square feet; the two convert exactly through the international pound and foot.
Your numbers, step by step
About the Grass Seed calculator
This grass seed calculator tells you how much seed to buy for a lawn and how many bags that comes to. Enter the area in square metres or square feet, choose whether you are sowing a new lawn on bare soil or overseeding an existing one, and type in the seeding rate printed on your seed bag. Bags usually give two rates, a heavier one for new lawns and a lighter one for overseeding, and the right figure depends on the grass species and mix, so the calculator never guesses it for you. It multiplies the rate by the area, adds an optional allowance for waste, rounds up to whole bags and shows the seed left over. Metric rates in g/m² and imperial rates in lb per 1,000 ft² are converted exactly, and every step of the working is shown.
How to use it
- Pick the “Units” and enter the “Lawn area”. For an odd shape, add up the rectangles that make it.
- Choose “New lawn” or “Overseeding” under “Seeding”.
- Type the matching rate from your seed bag into “Seeding rate for a new lawn” or “Seeding rate for overseeding”.
- Add any “Extra for edges and waste”, then the “Bag size” and, if you like, the “Price per bag (optional)”.
- Read the seed needed, the bags to buy and the seed left over in the last bag.
Worked example
A new lawn of 80 m², with a bag rate of 30 g/m² and 10% extra. Seed = 30 × 80 = 2,400 g = 2.4 kg, and with the extra 2.4 × 1.1 = 2.64 kg (about 5.82 lb). In 1 kg bags that is 2.64 ÷ 1 = 2.64, rounded up to 3 bags, with 0.36 kg left over. The same rate is 6.14 lb per 1,000 ft².
Updated
Questions people ask
How do I calculate how much grass seed I need?
Multiply the lawn area by the seeding rate on the bag. In metric, g/m² × m² ÷ 1000 gives kilograms; in imperial, lb per 1,000 ft² × ft² ÷ 1000 gives pounds.
Why is the overseeding rate lower than the new lawn rate?
Overseeding fills gaps in grass that is already growing, so it needs less seed than covering bare soil. Seed bags usually print both rates; use the one that matches the job.
What seeding rate should I use for my grass type?
Use the rate printed on the bag or the supplier's sheet for that exact product. Rates differ a lot between species and mixes, so this calculator asks you for the figure rather than suggesting one.
How do I convert g/m² to lb per 1,000 ft²?
Divide by 4.8824. One pound per 1,000 ft² is 453.59237 g spread over 92.90304 m², which is 4.8824 g/m².
Is it a mistake to measure the area roughly?
A rough guess can leave you short of seed. Measure the length and width of each part of the lawn, and use the square footage calculator to add up odd shapes before you start.
What does this grass seed estimate not cover?
It does not judge the soil, the season or the watering a new lawn needs. If you are preparing a new lawn, the topsoil calculator can size the soil, and a local garden centre can advise on timing for your climate.