Grass Seed Calculator

Last updated: June 2026

Lawn length

Lawn width

Seed rate

g/m2

Extra allowance

Lawn area

60 m2

Grass seed

2.21 kg

Formula

seed required = lawn area x seed rate x allowance / 1000.

About this calculator

The Grass Seed Calculator estimates seed quantity for new lawns, overseeding, patch repair, or garden renovation from lawn area, sowing rate, and waste allowance.

Grass Seed Calculator method

The calculator uses metric project dimensions, applies the material formula shown below, and then adds any waste or allowance entered. Quantities are rounded up where materials are normally purchased as whole boards, sheets, blocks, rolls, bags, or packs.

seed needed kg = area x sowing rate g per m2 / 1000
order seed = seed needed x (1 + waste percentage)

How to use the Grass Seed Calculator

Measure the lawn or patch area.
Choose new lawn or overseeding rate from the seed product.
Enter the sowing rate in grams per square metre.
Add waste for uneven spreading and patchy areas.
Round up to the nearest seed bag size.

Worked examples

New lawn seeding

Input: 60m2 lawn, 35g per m2, 10% waste

Calculation: 60 x 35 / 1000 x 1.10

Result: About 2.31kg of grass seed.

Overseeding

Input: 80m2 lawn, 20g per m2

Calculation: 80 x 20 / 1000

Result: About 1.6kg before waste.

When this calculator is useful

The Grass Seed Calculator estimates seed quantity for new lawns, overseeding, patch repair, or garden renovation from lawn area, sowing rate, and waste allowance.

Use it before ordering materials, comparing supplier pack sizes, or checking whether a first estimate is realistic. Keep the result with your measured dimensions so you can update the calculation if the project size changes.

Inputs that affect the result

Seed mix: Shade, hard-wearing, ornamental, and drought-tolerant mixes can have different rates.
Preparation: Soil preparation, watering, and timing strongly affect germination.
Overseeding: Overseeding usually uses a lower rate than a new lawn.

Common mistakes to avoid

Check 1: Birds, poor watering, compaction, and cold soil can reduce success.
Check 2: Very patchy lawns may need renovation rather than light overseeding.
Check 3: Product labels should override generic sowing rates.

Material planning notes

Planning point	Why it matters
Measure finished area	Use the actual finished dimensions after allowing for openings, edges, posts, slopes, or returns.
Allow for waste	Cuts, breakages, joins, pattern matching, awkward shapes, and site handling usually mean ordering more than the exact calculated amount.
Round purchase quantities up	Most materials are bought as full boards, sheets, bags, blocks, rolls, packs, or bulk deliveries.
Check supplier specifications	Coverage, density, sheet size, block size, and pack size vary by product and supplier.

Limitations and safety

This calculator is for general project planning only. It does not replace a structural design, building regulations advice, manufacturer instructions, supplier specifications, or a competent tradesperson. Projects involving structure, roofs, retaining walls, foundations, drainage, electrics, gas, or safety-critical work should be checked properly before buying materials or starting work.

Frequently asked questions

Should I order exactly the calculated quantity?

Usually no. Order in the nearest practical pack, board, sheet, bag, roll, or delivery quantity, and keep a sensible waste allowance for cuts and mistakes.

What waste allowance should I use?

Simple rectangular jobs may only need 5-10%. Patterned, angled, fragile, or irregular projects may need more. The right allowance depends on the material and layout.

Why might my supplier quantity differ?

Suppliers use specific product sizes, densities, coverage rates, and pack quantities. Use the calculator as a planning estimate, then compare it with the product label or datasheet.

Can I use this for professional building work?

It can help with a rough take-off, but professional work should be checked against drawings, specifications, site conditions, and relevant UK rules or standards.

What measurements should I double-check?

Check length, width, depth, height, spacing, openings, pitch, and units. A small unit mistake can change a material order by a large amount.

Related calculators

turf-calculator
soil-calculator
mulch-calculator

What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.