How to measure your pour
Measure the finished outside dimensions of the forms, not the area you dug. For a slab, measure length and width in feet and the thickness in inches. Check the depth in several places: a slab you planned at 4 in but dug unevenly can average 4.5 in, which is 12.5% more concrete.
For footings and walls, add up the total run of all footing segments (a 20 × 30 ft rectangle has 100 ft of footing) and enter the width and depth in inches. For post holes and round columns, enter the hole diameter and depth, then set the number of identical holes.
Worked example: a 10 × 10 ft patio
| Step | Calculation | Result |
|---|---|---|
| Volume | 10 ft × 10 ft × (4 in ÷ 12) | 33.33 cu ft |
| Convert to yards | 33.33 ÷ 27 | 1.23 cu yd |
| Add 10% waste | 1.23 × 1.10 | 1.36 cu yd (36.7 cu ft) |
| 80 lb bags | 36.7 ÷ 0.60 | 62 bags |
| Ready-mix order | round up to ¼ yd | 1.5 cu yd |
At late-2026 typical prices, 62 bags cost about $350, while 1.5 yd of ready-mix is about $195 plus a short-load fee that can easily double the bill for a small order. That’s why the calculator compares both options with your own prices.
Bags or a ready-mix truck?
- Under about 1 cu yd (roughly 45 × 80 lb bags): bags are usually cheaper and simpler. A wheelbarrow and a hoe or a rented drum mixer is enough.
- 1–3 cu yd: it depends on your plant’s minimum order and short-load fee. Call two local suppliers; some offer small “mini-mix” trucks or trailer loads without heavy fees.
- Over 3 cu yd: ready-mix almost always wins. Hand-mixing 135+ bags before the first ones start to set is very hard to do well.
Remember the hidden costs of bags: delivery or several trips, a mixer rental, and labor. The calculator compares material cost only.
How much extra should you order?
Running short in the middle of a pour creates a cold joint, a weak seam where fresh concrete meets concrete that has already started to set. Professionals typically order 5–10% extra: 5% for formed slabs on a well-compacted, level base, and 10% or more for uneven ground, thickened slab edges or footings dug in soil. The scenario table shows the volume and bag count at 0%, 5%, 10% and 15% so you can choose.
What this calculator doesn’t include
Gravel base (see the gravel calculator), rebar or wire mesh, form lumber, a pump truck (often needed when the truck can’t get within about 20 ft of the pour), finishing labor, sealing, and permits. For a full installed price, local contractors in 2026 commonly quote roughly $6–$12 per sq ft for a basic 4 in slab, depending on access, site prep and finish.
How this calculator works
- Slab volume = length × width × (thickness ÷ 12). Footing volume = length × (width ÷ 12) × (depth ÷ 12). Column volume = π × (diameter ÷ 24)² × height.
- Total volume is multiplied by (1 + waste%) and converted from cubic feet to cubic yards by dividing by 27.
- Bags are rounded up to whole bags; ready-mix is rounded up to the next ¼ cu yd, and a short-load fee is charged for each cubic yard below the truck minimum.
Assumptions and limitations
- Bag yields use manufacturer figures: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft.
- Ready-mix is ordered in ¼ cu yd increments. The short-load fee is charged per cubic yard below the truck minimum.
- Prices are national typical retail/plant prices for late 2026 — replace them with your local quotes.
- Costs cover material only: no forms, gravel base, rebar/mesh, pump truck or labor.
These results are planning estimates, not quotes. Local prices, site conditions and building codes vary, so get written estimates from licensed contractors before you commit to a budget.
Try your own numbers. Every price and assumption above is editable in the estimator.
Back to the concrete estimatorFrequently asked questions
How many 80 lb bags of concrete make a yard?
How thick should a concrete slab be?
When is ready-mix cheaper than bags?
Sources and data
- HomeGuide (2026) — concrete prices
- Angi (2026) — how much does it cost deliver concrete
- Quikrete data sheet (Concrete Mix No. 1101)
- ShopSavvy price tracker (Lowe's listing) — quickrete 80lb concrete mix
- HomeGuide (2026) — concrete slab cost
Prices are US national ranges reviewed October 2026 (data version 2026.10). A few values are editorial estimates where no single published source exists; the Cost Index marks each one. Read our methodology and editorial policy.