# BuildCalc Journal

> Free construction calculators and plain-English estimating guides: concrete, slabs, blocks, rebar and more, for US, UK, Australia and New Zealand.

## Calculators & Guides
- [Concrete Slab Calculator: How Much Concrete Do You Need?](https://example.com/blog/concrete-slab-calculator): Free concrete slab calculator for yards, m³ and bags. Learn the formula, add waste, compare bags vs ready-mix and estimate cost for US, UK, AU & NZ.
  Quick answer: Multiply length × width × thickness (in feet) to get cubic feet, divide by 27 for cubic yards, and add 5–10% waste. A 10 × 10 ft slab at 4 in thick needs 1.23 yd³ net (1.36 yd³ with 10% waste, or ~62 bags of 80-lb mix). In metric, L × W × T in metres gives m³ directly.
- [Concrete Block Wall Calculator: Cinder Block, CMU, Mortar & Grout](https://example.com/blog/concrete-block-wall-calculator): Free cinder block & CMU wall calculator. Estimate 8×8×16 blocks, UK 440 mm & AU/NZ 20-series blocks, mortar bags, core-fill grout and wall cost.
  Quick answer: Multiply wall length × height, subtract openings, and multiply net square feet by 1.125 for standard 8×8×16 in CMU blocks (or 10 blocks/m² in the UK and 12.5 blocks/m² in Australia & NZ), then add 5–10% waste. Budget ~3 bags of 80-lb mortar per 100 blocks.
- [Footing & Sonotube Concrete Calculator: Piers, Post Holes & Strip Footings](https://example.com/blog/footing-sonotube-calculator): Calculate cubic yards, m³ and 80-lb or 60-lb concrete bags for round Sonotube piers, fence post holes (subtracts post volume) and strip footings.
  Quick answer: For round Sonotube piers, use V = π × (diameter ÷ 2)² × depth. A 12-inch tube 4 feet deep holds 3.14 ft³ (0.12 yd³), or 6 bags of 80-lb concrete with waste. For fence posts, subtract the buried post volume from the auger hole cylinder.
- [Concrete Slab Rebar Calculator: Grid Spacing, Bar Count & Laps](https://example.com/blog/rebar-slab-calculator): Free rebar calculator for concrete slabs and driveways. Calculate #3–#6 or metric H10–H16 bar count, 40d lap splices, chairs, wire ties and steel weight.
  Quick answer: Subtract twice the 3-inch (75 mm) edge cover from slab length and width, divide each span by your on-center spacing and add 1 to get runs each way. Add 40 bar diameters per lap splice on runs over 20 ft (6 m), plus 10% offcut waste.
- [Concrete Driveway Cost Calculator: Installed Price, Volume & Sub-Base](https://example.com/blog/concrete-driveway-cost-calculator): Estimate concrete driveway cost per sq ft or m² in the US, UK, Australia & NZ. Compare broom, exposed aggregate & stamped finishes plus ready-mix volume.
  Quick answer: An installed broom-finished concrete driveway typically runs $8–$14/ft² in the US (£90–£140/m² UK, A$110–A$160/m² AU, NZ$130–NZ$185/m² NZ) including compacted gravel base and reinforcement. Exposed aggregate and stamped finishes add 30–75%.

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