How much concrete do I need for a slab?

Multiply length × width × thickness (convert thickness to feet or meters). Add 5–10% waste.

What waste factor should I use?

Common practice is 5–10% for small pads and 3–5% for larger, simpler pours.

How many 80-lb bags make 1 cubic yard?

About 45 bags of 80 lb mix per cubic yard (based on typical yield).

Do I need rebar or wire mesh?

For slab-on-ground, welded wire reinforcement or deformed bars at regular spacing help control cracking. Follow local codes and a licensed engineer.

What concrete strength should I use?

Most residential slabs use 3000–4000 psi (20–28 MPa), but climate, exposure, and loads may require different specs per ACI and local code.

How much does ready-mix cost?

Varies by region and mix; enter your local cost per cubic yard or per cubic meter to estimate.

Project Layout & Design — Concrete Slab Calculator

Calculate concrete volume, bag counts, weight, rebar/mesh, and cost for slab-on-ground projects. Mobile-first, WCAG-compliant calculator for contractors and homeowners.

Full original guide (expanded)

CalcDomain

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

\[V = L \times W \times T\]

V = L \times W \times T

Formula (extracted LaTeX)

\[T_\text{ft} = \begin{cases} \frac{T_\text{in}}{12} & \text{(imperial)}\\[4pt] \frac{T_\text{cm}}{100} & \text{(metric)} \end{cases} \quad V_\text{yd}^3 = \frac{V_\text{ft}^3}{27} \quad V_{\text{m}^3} = V_\text{m}^3\]

T_\text{ft} = \begin{cases} \frac{T_\text{in}}{12} & \text{(imperial)}\\[4pt] \frac{T_\text{cm}}{100} & \text{(metric)} \end{cases} \quad V_\text{yd}^3 = \frac{V_\text{ft}^3}{27} \quad V_{\text{m}^3} = V_\text{m}^3

Formula (extracted LaTeX)

\[V_\text{net} = V \times \left(1 + \frac{w}{100}\right)\]

V_\text{net} = V \times \left(1 + \frac{w}{100}\right)

Formula (extracted LaTeX)

\[\text{Bags}_{80} \approx 45 \times V_\text{yd}^3 \quad \text{Bags}_{60} \approx 60 \times V_\text{yd}^3 \quad \text{Bags}_{40} \approx 90 \times V_\text{yd}^3\]

\text{Bags}_{80} \approx 45 \times V_\text{yd}^3 \quad \text{Bags}_{60} \approx 60 \times V_\text{yd}^3 \quad \text{Bags}_{40} \approx 90 \times V_\text{yd}^3

Formula (extracted LaTeX)

\[\text{Weight} \approx \rho \times V_\text{net} \quad \text{with } \rho \approx \begin{cases} 150\ \text{lb/ft}^3 & \text{(2400 kg/m}^3) \end{cases}\]

\text{Weight} \approx \rho \times V_\text{net} \quad \text{with } \rho \approx \begin{cases} 150\ \text{lb/ft}^3 & \text{(2400 kg/m}^3) \end{cases}

Formula (extracted text)

\[ V = L \times W \times T \] \[ T_\text{ft} = \begin{cases} \frac{T_\text{in}}{12} & \text{(imperial)}\\[4pt] \frac{T_\text{cm}}{100} & \text{(metric)} \end{cases} \quad V_\text{yd}^3 = \frac{V_\text{ft}^3}{27} \quad V_{\text{m}^3} = V_\text{m}^3 \] \[ V_\text{net} = V \times \left(1 + \frac{w}{100}\right) \] \[ \text{Bags}_{80} \approx 45 \times V_\text{yd}^3 \quad \text{Bags}_{60} \approx 60 \times V_\text{yd}^3 \quad \text{Bags}_{40} \approx 90 \times V_\text{yd}^3 \] \[ \text{Weight} \approx \rho \times V_\text{net} \quad \text{with } \rho \approx \begin{cases} 150\ \text{lb/ft}^3 & \text{(2400 kg/m}^3) \end{cases} \]

Variables and units

No variables provided in audit spec.

Sources (authoritative):

NRMCA — National Ready Mixed Concrete Association — nrmca.org · Accessed 2026-01-19
https://www.nrmca.org/
ACI — American Concrete Institute — concrete.org · Accessed 2026-01-19
https://www.concrete.org/

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
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Formulas

(Formulas preserved from original page content, if present.)

Version 0.1.0-draft

Citations

Add authoritative sources relevant to this calculator (standards bodies, manuals, official docs).

Changelog

0.1.0-draft — 2026-01-19: Initial draft (review required).