Concrete Bench Calculator
Estimate concrete for a poured concrete bench seat and its supports.
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Short answer
A typical public-style concrete bench — a 72×18×4 inch seat on two 18×6×16 inch supports — needs about 3.5 cubic feet of concrete, or roughly 6 bags of 80 lb premix. Larger benches or ones with solid concrete pedestal bases will need proportionally more.
Typical concrete bench dimensions
| Bench part | Typical size | Notes |
|---|---|---|
| Seat slab | 60–96 in long, 14–20 in wide | 3–4 in thick is typical |
| Support / leg | 14–20 in wide, 4–8 in deep | 16–18 in tall for standard seat height |
| Pedestal base (solid) | Full width, 6–12 in deep | Used instead of individual legs on some designs |
How to plan a concrete bench pour
- Decide on seat length, width, and thickness, and whether you want two end supports or a full pedestal base.
- Enter your dimensions above to get total volume, cubic yards, and bag count.
- Reinforce the seat slab with rebar or wire mesh, especially for spans longer than 4 feet, to prevent sagging and cracking.
- Build or rent forms for the seat and supports; a smooth or textured form liner controls the finished look.
- Pour supports first (or same day) and let them set enough to support the seat slab if poured separately.
- Cure for at least 7 days before use, and seal the surface after 28 days to protect against staining and weathering.
Worked example
- Seat
- 72 × 18 × 4 in = 5,184 in³ = 3.0 ft³
- Supports
- 2 × (18 × 6 × 16 in) = 3,456 in³ = 2.0 ft³
- Total with 10% waste
- (3.0 + 2.0) × 1.10 = 5.5 ft³
- Bags (80 lb, 0.60 ft³ each)
- ceil(5.5 / 0.60) = 10 bags
Common mistakes
- Skipping rebar or mesh in the seat slab, which cracks under weight and thermal movement over time.
- Undersizing supports so the bench feels unstable or rocks when sat on.
- Forgetting to account for multiple benches when ordering material for a park or patio project.
- Not sealing the finished surface, leading to staining and faster weathering outdoors.
Assumptions
- Standard concrete at roughly 150 lb per cubic foot.
- Bag yields follow manufacturer averages: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 50 lb = 0.375 ft³, 40 lb = 0.30 ft³.
- Assumes two rectangular end supports; adjust the support count to 0 if using a different base style.
- Does not include rebar, mesh, forms, sealant, or finishing materials.
Frequently asked questions
Does a concrete bench need rebar?
Yes, for most designs. A seat slab spanning more than about 4 feet between supports should have rebar or welded wire mesh to resist cracking and sagging under repeated loads.
How thick should a concrete bench seat be?
3 to 4 inches is standard for a bench seat. Thinner slabs are prone to cracking, especially without reinforcement.
Can I pour the seat and supports at the same time?
Yes, if you build one connected form for the whole bench and pour it in a single continuous pour, which also gives a stronger, crack-resistant result than pouring in stages.