Grass Seed Calculator
Enter your lawn’s length and width (or diameter) to find out exactly how many pounds, bags, and dollars of grass seed you’ll need.
Prefilled from the selected product — adjust to match your bag label or soil test.
Covers uneven application and edges. 5–10% is normal.
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Application tips
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Rate & coverage
Product profile
For a 50 × 100 ft lawn (5,000 sq ft) using overseeding mix at 6 lb per 1,000 sq ft with 5% waste, you need 31.5 lb of seed, which rounds up to 2 bags (25 lb each). At $45 per bag, that’s about $90 in materials.
Grass seed needed for common lawn projects
Quantities include a 5% waste allowance for spreader overlap and uneven coverage.
| Project size | Seed type | Amount needed | Bags |
|---|---|---|---|
| Bare-spot repair, 10 × 10 ft (100 sq ft) | Patch & repair mix | 0.84 lb | 1 bag |
| New lawn, small yard, 30 × 40 ft (1,200 sq ft) | New lawn seed mix | 20.16 lb | 1 bag |
| Overseeding, average lawn, 50 × 100 ft (5,000 sq ft) | Overseeding mix | 31.50 lb | 2 bags |
| New lawn, average size, 50 × 100 ft (5,000 sq ft) | New lawn seed mix | 84.00 lb | 4 bags |
| New lawn, large yard, 60 × 120 ft (7,200 sq ft) | New lawn seed mix | 120.96 lb | 5 bags |
| New lawn, big property, 80 × 150 ft (12,000 sq ft) | New lawn seed mix | 201.60 lb | 9 bags |
How to calculate grass seed you need
- Measure your lawn area. length × width in feet for a rectangular lawn, or radius² × π for a circular one.
- Choose your seeding purpose and rate. New lawns need a much higher seeding rate (around 16 lb per 1,000 sq ft) than overseeding an existing lawn (around 6 lb per 1,000 sq ft).
- Scale the rate to your area. Divide your area by 1,000, then multiply by the seeding rate to get the raw pounds needed.
- Add waste for uneven coverage. Multiply by 1 plus your waste percentage — 5% covers spreader overlap and touch-up seeding on thin spots.
- Round up to full bags. Divide total pounds by the bag size and round up — you can’t buy a partial bag.
Worked example
Using the calculator’s default 50 ft × 100 ft lawn with overseeding mix at 6.0 lb per 1,000 sq ft, 5% waste, $45 per 25 lb bag:
- Area50 ft × 100 ft = 5,000 sq ft
- Rate6.0 lb per 1,000 sq ft
- Raw pounds needed(5,000 ÷ 1,000) × 6.0 = 30.0 lb
- Plus 5% waste30.0 × 1.05 = 31.5 lb
- Bag size25 lb
- Bags needed (31.5 ÷ 25, rounded up)2 bags
- Total estimated cost$90.00
Choosing a grass seed type
Match the seed mix and seeding rate to the condition of the ground you’re planting into.
- New lawn seed mixEstablishing a lawn from bare soil — applied at a much higher rate (around 16 lb per 1,000 sq ft) to ensure full coverage with no existing turf.
- Overseeding mixThickening an existing lawn — applied at a lower rate (around 6 lb per 1,000 sq ft) since living turf already covers most of the ground.
- Patch & repair mixBare or thin spot repair — usually includes mulch or a tackifier to hold seed in place and retain moisture in a small area.
- Cool-season vs. warm-season blendsMatch your seed’s grass species to your climate zone — fescue and ryegrass for cool regions, Bermuda and zoysia for warm regions.
- Sun and shade formulationsMany mixes are blended specifically for full sun or shaded areas — using the wrong blend can lead to thin, patchy establishment.
Common mistakes
- Using a new-lawn rate for overseeding.Overseeding an existing lawn needs far less seed than starting from bare soil — applying the higher rate wastes seed and can smother existing turf.
- Skipping the waste allowance.Spreader overlap and thin-spot touch-ups both consume extra seed — a 5% waste allowance avoids running short mid-project.
- Seeding at the wrong time of year.Cool-season grasses establish best in early fall or spring; seeding in peak summer heat often leads to poor germination and heat stress.
- Not matching seed blend to sun exposure.A full-sun blend planted in a shaded yard (or vice versa) will struggle regardless of how carefully you calculated the quantity.
- Skipping soil prep before seeding.Seed-to-soil contact matters more than seed quantity — raking, aerating, or topdressing improves germination rates significantly.
- Ignoring bag coverage claims blindly.Bag labels often list a ‘new lawn’ and ‘overseed’ coverage rate — make sure you’re using the rate that matches your actual project, not just the bigger number.
What this calculator assumes
Adjust your result if your project differs from these.
- Seeding rate is based on pounds of seed per 1,000 sq ft, per the product’s labeled rate for new lawn vs. overseeding use.
- A 5% waste allowance covers standard spreader overlap and touch-up seeding on thin areas.
- Lawn area is measured as usable turf area, excluding beds, paths, and structures.
- Circular lawn area is calculated as π × radius².
- Bag sizes (25 lb for most blends, 10 lb for patch mixes) reflect common retail packaging — confirm against the specific product you’re buying.
- This calculator estimates seed quantity only and does not account for soil preparation, starter fertilizer, or irrigation needs.
Common questions
How much grass seed do I need for a 5,000 sq ft lawn?
For overseeding at 6.0 lb per 1,000 sq ft with 5% waste, you need 31.5 lb of seed, which rounds up to 2 bags of 25 lb. For a full new lawn at 16 lb per 1,000 sq ft, you’d need about 84 lb, or 4 bags.
What's the difference between new lawn and overseed rates?
New lawn seeding rates (around 16 lb per 1,000 sq ft) are roughly 2-3x higher than overseeding rates (around 6 lb per 1,000 sq ft) because there’s no existing turf to fill in gaps.
How do I calculate seed for a circular lawn area?
Multiply the radius by itself, then by π (about 3.1416) to get the area, then apply the same rate-per-1,000-sq-ft formula.
Should I add waste when calculating grass seed?
Yes — 5% is a reasonable default to cover spreader overlap and extra seeding on thin or bare patches.
How much seed do I need for a bare patch repair?
For a small 10 × 10 ft patch at a patch-mix rate of 8 lb per 1,000 sq ft, you’d need under 1 lb — still round up to a full bag since patch mixes are often sold in small 10 lb bags.
When is the best time to plant grass seed?
Early fall is ideal for cool-season grasses; late spring through early summer is best for warm-season grasses, once soil has warmed.
Does bag size affect how much seed I need?
No — total pounds needed stays the same regardless of bag size, but bag size determines how many bags you round up to.
How many bags of grass seed do I need for an acre?
An acre is about 43,560 sq ft; for a new lawn at 16 lb per 1,000 sq ft with 5% waste, that’s roughly 731 lb, or about 30 bags of 25 lb seed.
Can I mix seed types in one lawn?
It’s best to use one consistent blend per project so germination timing and grass appearance match across the whole area.
Do I need starter fertilizer with new grass seed?
Yes, it’s recommended — starter fertilizer’s higher phosphorus content supports root development in newly germinating seed, separate from this seed calculation.
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Notes
Estimate generated by materialcalculate.com. Confirm quantities and rates with your product label before ordering.