Concrete Calculator
Adjust the inputs below. Results update as you type.
How it works
Volume = length × width × depth for rectangular slabs. Convert inches to feet before multiplying (1 in = 1/12 ft). Divide cubic feet by 27 for cubic yards. Add 5–10% waste factor for spillage and irregular forms. One cubic yard of ready-mix weighs ~4,000 lb. Standard residential slabs use 3,000–4,000 PSI mix; structural footings often require 4,000+ PSI.
Input guidance
- Confirm date/time/unit settings before comparing outputs.
- If a task has optional fields, run both with and without them to understand impact.
- Save scenario variants when making practical decisions.
The formula
Concrete volume = length × width × thickness, converted to cubic yards (÷ 27 for feet) or cubic meters. Add about 5–10% for waste and spillage.
Worked example
A slab 10 ft × 10 ft × 4 in (0.33 ft) = 33.3 cubic feet ÷ 27 ≈ 1.23 cubic yards; order about 1.35 yards to allow for waste.
More examples to test
- Quick-pass example: run default assumptions for a first estimate.
- Refined example: update one assumption at a time to isolate impact.
How to interpret results
Use outputs as operational estimates and pair them with local constraints, business rules, or provider requirements.
When this can be inaccurate
Utilities can miss local policy details, special-case rules, and environment-specific constraints.
Change history
- June 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
How much concrete do I need?+
Multiply length × width × thickness in consistent units, convert to cubic yards or meters, and add a margin for waste.
Why add extra?+
Spillage, uneven subgrade, and form variations mean actual use exceeds the exact calculation, so 5–10% extra avoids running short.
How many bags equal a yard?+
It takes roughly 45 eighty-pound bags of premixed concrete to make one cubic yard — bulk delivery is cheaper for large pours.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.
Guided next steps
Want the full workflow? Use this calculator inside a step-by-step guide.