Concrete Calculator

DIY homeowner — 10 × 10 patio

• Shape: slab
• Length: 10 ft
• Width: 10 ft
• Thickness: 4 in
• Waste: 10% · Bag size: 80 lb

Output: 1.23 yd³ net · 1.36 yd³ with waste · 62 × 80 lb bags (~$465–$650) · ready-mix all-in ~$300–$520

At 1.36 yd³ you're below ready-mix minimums in most markets — the short-load surcharge ($53/yd³) and delivery fee ($60–$180) push the truck total above $300. Bag mixing is competitive on price but 62 bags is about 9 hours of mixing with a small electric mixer; rent a tow-behind mixer or split the pour into thirds.

Contractor — 20 × 24 driveway, 5 in

• Shape: slab
• Length: 24 ft
• Width: 20 ft
• Thickness: 5 in
• Waste: 8%

Output: 7.41 yd³ net · ~8.0 yd³ with waste · ~$1,000–$1,560 concrete + $60–$180 delivery

Above 7 yd³ ready-mix wins decisively. Order a full 8 yd³ truck — you're past the short-load threshold so no $53/yd³ surcharge applies; leftover concrete gets dumped on subgrade prep area. At 5 in, this is rated for cars and light trucks per Concrete Network's driveway-thickness guide.

Fence builder — 22 post holes

• Shape: column / hole
• Diameter: 10 in
• Depth: 30 in
• Quantity: 22
• Waste: 10%

Output: 0.051 yd³ per hole (full cylinder) · total 1.22 yd³ with waste · ~74 × 60 lb bags

Volume per hole is small but multiplies fast: 22 posts ≈ 1.22 yd³ with 10% waste, just above 1 yd³. Bag setting (the no-mix QUIKRETE method — pour dry mix, then water) saves labor for runs under 30 posts. The 4 × 4 wood post displaces about 0.014 ft³ per hole; the calculator's full-cylinder result is conservatively over-estimated, which is fine — extra mix becomes the post collar.

Architect — 6 ft fire-pit base, 6 in

• Shape: circular slab
• Diameter: 6 ft
• Thickness: 6 in
• Waste: 10%

Output: 0.524 yd³ net · 0.576 yd³ with waste · ~26 × 80 lb bags (~$195–$275)

Circular forms generate small volumes — under 1 yd³ here. Bags win on cost. Cut a sonotube or a wood form first; manual radial screeding is essential because slab thickness directly controls thermal cracking under the heat of a fire pit.

Deck builder — 12 cylinder footings

• Shape: column
• Diameter: 12 in
• Height: 48 in below frost line
• Quantity: 12
• Waste: 10%

Output: 0.116 yd³ per footing · total 1.54 yd³ with waste · ~93 × 60 lb bags or ~70 × 80 lb

1.54 yd³ over 12 footings is bag territory because each pour is spaced 30+ minutes apart for screeding and leveling. A single ready-mix truck would harden in the chute before all footings are placed. Confirm the 48 in depth meets your local frost line — northern states require 36–48 in; the Deep South often only requires 12 in.

1. Forgetting to convert inches to feet

A 10 × 10 × 4 in slab is not 400 cubic units of anything useful. The 4 in must become 0.333 ft before multiplication, otherwise the result is 400 instead of 33.33 ft³ — off by a factor of 12. This calculator labels each input with its unit and converts internally so you can enter feet and inches naturally.

2. Applying waste to volume but not to bag count

A 1.23 yd³ slab with 10% waste = 1.36 yd³ for ready-mix ordering, but the bag count must also be calculated from the waste-inclusive volume. Otherwise the homeowner runs short by 10% mid-pour and the slab fails. This calculator applies waste before dividing by bag yield — every time.

3. Ignoring the short-load surcharge

Ready-mix pricing flips above ~5 yd³. For 0.5–4 yd³ jobs, the short-load surcharge ($53/yd³) often makes bags cheaper despite the labor cost. We surface this fee automatically when your volume is below the threshold so the real ready-mix vs. bag economics are visible.

4. Setting footings above the frost line

In northern US states, footing depth must extend below the local frost line (24–48 in). A user inputting '12 in deep' for a footing in Minnesota will get a code-non-compliant result. The calculator computes any depth you enter — but check local code; we cannot infer your zone from inputs alone.

5. Hollow vs. solid for tube / pipe forms

A 12 in diameter sonotube is solid; a 12 in pipe with a 1 in wall is hollow. Treating a hollow tube as solid overshoots concrete by 50%+. For hollow forms, calculate the outer cylinder, then calculate the inner cylinder with the column tab and subtract — or use the formula V = π × (R² − r²) × h directly.

6. Diameter vs. radius confusion on round columns

Users routinely enter '6 in radius' meaning '6 in diameter' and over-pour by 4× (radius squared compounds the error). This calculator labels the input as diameter explicitly, then shows you the converted radius in the formula trail so you can verify.

7. Stair nosing not modeled

Concrete stairs include a nosing overhang (~1 in) that adds non-trivial volume. For 12-step stairs at 36 in wide, nosing alone adds ~0.05 yd³. Our solid-stair calculation uses the stacked-rectangle (closed-riser) method — V = run × rise × width × N(N+1)/2 — which is correct for site-cast stairs without nosings. If your design has nosings, add roughly 5% to the result.

8. Rounding bag counts down instead of up

Math.round(8.2) returns 8 — so you arrive on pour day one bag short. Always Math.ceil for bag counts. We apply ceiling on every bag-size column so an 8.2 calculation becomes 9 every time. Cubic-yard display still rounds normally to 0.01 because pouring 1.23 vs. 1.234 yd³ changes nothing at the truck.