What does the Lawn Seed Calculator do?

Calculate grass seed needed for new lawns, overseeding or repair. Get bag counts and cost estimates. All calculations are performed in your browser using official UK rates and thresholds.

Does this include delivery costs?

This calculator estimates material quantities and approximate costs. Delivery charges vary by supplier, quantity and location. Bulk orders often qualify for free or reduced delivery.

When is the best time for this project?

Timing depends on the specific project. Generally, spring and autumn are ideal for lawn and planting work, while hard landscaping can be done year-round in dry conditions.

Lawn Seed Calculator

Calculate grass seed needed for new lawns, overseeding or repair. Get bag counts and cost estimates.

Last updated: April 2026 · Source: RHS — Growing a lawn from seed

Purpose

Length (m)

Width (m)

Seed Price (£/kg)

Seed Needed

2.8 kg

1kg Bags

Lawn Area

80 m²

Est. Cost

£42.00

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Grass seed application rates depend on whether you are creating a new lawn or overseeding an existing one. For new lawns, the typical rate is 35–50 g per m². For overseeding (repairing patches or thickening thin areas), 15–25 g per m² is sufficient. Premium seed mixes with ryegrass tend to use higher rates; fine fescue mixes use lower rates.

This calculator takes your lawn area and purpose to estimate the total weight of seed needed. It also accounts for different seed types: hard-wearing utility mixes (ideal for families and pets), fine ornamental mixes (for low-traffic lawns) and shade-tolerant mixes. Each has a slightly different recommended sowing rate.

The best time to sow grass seed in the UK is April–May or September–October, when soil temperatures are above 8–10°C. Keep the area moist for 2–3 weeks after sowing. Enter your lawn dimensions and choose new lawn or overseed to see the quantity and estimated cost.

Example: New lawn, 50 m², hard-wearing utility mix

Recommended rate: 40 g/m²
Total seed: 50 × 40 = 2,000 g = 2 kg
Add 10% for edges and uneven coverage: 2.2 kg
Estimated cost: £15–£25 for a 2.5 kg box

Source: RHS — Growing a lawn from seed

Frequently Asked Questions

What does the Lawn Seed Calculator do?: Calculate grass seed needed for new lawns, overseeding or repair. Get bag counts and cost estimates. All calculations are performed in your browser using official UK rates and thresholds.
Does this include delivery costs?: This calculator estimates material quantities and approximate costs. Delivery charges vary by supplier, quantity and location. Bulk orders often qualify for free or reduced delivery.
When is the best time for this project?: Timing depends on the specific project. Generally, spring and autumn are ideal for lawn and planting work, while hard landscaping can be done year-round in dry conditions.