Sources & formulas

Every calculator on CementCalcs rests on established arithmetic plus stable concrete conventions. Unlike topics with a time dependency, “verification” here is mathematical: each formula is tested against known values and is therefore correct for good. Here are the technical foundations by area.

Identities & geometry

  • Volume: slab volume (cu ft) = area (sq ft) × (thickness_in ÷ 12); a tube/column = π × (diameter ÷ 24)² × height; steps = Σ of riser/tread prisms.
  • Unit identities: 1 cubic yard = 27 cubic feet; gravel ≈ 1.4 tons per yd³; whole units (bags, blocks) always round up with ceil().

Quantity conventions (labeled typicals)

  • Bag yield: a 40 lb bag ≈ 0.30, a 60 lb ≈ 0.45, an 80 lb ≈ 0.60 ft³ — labeled, confirm on your bag.
  • Coverage per yard: 1 yd³ covers ~65 sq ft at 3", ~46.7 at 4", ~35 at 6" — geometry (27 ÷ thickness in feet).
  • Slab thickness: 4" residential slab/patio/sidewalk, 4–5" garage/shed, 5–6" driveway/heavy — labeled planning bands, not a structural design.
  • Rebar & sub-base: #3–#4 bar (or mesh) at 12–18" o.c. with ~10% lap; sub-base ~4–6" compacted gravel — labeled typicals.
  • Block & mortar: a standard 8×16 block covers ≈ 0.888 sq ft with joint; ≈ 3 mortar bags per 100 block — labeled.
  • Sealer: ~150–250 sq ft per gallon per coat — labeled, confirm on the can.

Cost tools

  • Every cost tool uses the prices you enter ($/yd³, $/sq ft, $/bag, $/lf, $/gal, $/step, delivery/short-load/pump/haul $) — no ready-mix or labor price is stored, so the site needs no maintenance. Cost bands are a labeled sanity guide.
  • Flatwork cost: total = (area × $/sq ft + sub-base + rebar + add-ons − discount) ×(1 + contingency).
  • Repair / leveling: total = area or lineal × your $/unit; resurfacing = (area × $/sq ft + coating) ×(1 + contingency).

Ready-mix and labor prices, product yields, permit rules and local code vary by place and change over time — always confirm yield against your product’s bag/spec sheet, order a little extra (5–10%) for spillage and uneven subgrade, and get itemized written quotes from a licensed, insured concrete contractor (and, for load-bearing work, a licensed engineer) before you commit.