Concrete Calculator: Combined Footing (Two Columns)

Estimate concrete for a two-column combined footing. Choose a rectangular or trapezoidal plan with constant thickness, set quantity and waste allowance, and (optionally) add pedestals under each column. Results show footing-only, pedestal total, and grand total volumes in m³, yd³, and ft³, with approximate bag counts. Notes, formulas, and FAQs included.

Units Metric (m, mm) US Customary (ft, in)

Footing plan type

Number of footings

pcs

Waste allowance

Covers spillage, over-excavation, and dimensional variation.

Length L

Width B

Thickness T

Add pedestals under columns (optional)

Column A pedestal

Column B pedestal

Pedestals are assumed to sit on top of the footing; heights project above the footing top.

Results

Footing volume (per piece)

0.000 m³

0.000 yd³

0.00 ft³

Pedestal volume (per piece)

0.000 m³

0.000 yd³

0.00 ft³

Total with waste

0.000 m³

0.000 yd³

0.00 ft³

Approximate bag counts (total with waste)

US bag sizes (QUIKRETE® yield)

40 lb bag00.30 ft³ per bag

50 lb bag00.375 ft³ per bag

60 lb bag00.45 ft³ per bag

80 lb bag00.60 ft³ per bag

90 lb bag00.675 ft³ per bag

Yields per bag from QUIKRETE data sheet. Actual yield varies with placement and compaction. Source

Metric bag sizes

Edit yields to match your local supplier data.

20 kg bag yield m³ 25 kg bag yield m³ 40 kg bag yield m³

20 kg bag0

25 kg bag0

40 kg bag0

How to use this concrete calculator

Select metric or US units.
Pick the plan type (rectangular or trapezoidal) and enter length, width(s), and thickness.
Set the quantity and waste allowance. Many jobs add 4–10%.
Optional: add pedestals for Column A and Column B (rectangular or circular) with heights above the footing.
Read per-piece and total volumes, then review bag counts for ordering. Round up.

Formulas and assumptions

Rectangular plan (constant thickness): V = L × B × T.
Trapezoidal plan (constant thickness): plan area A = L × (B₁ + B₂)/2, so V = A × T = L × (B₁ + B₂) × T / 2.
Pedestals (each): rectangular V = B × D × H; circular V = π(D/2)² × H.
Total: V_piece = V_footing + V_{pedestals (A+B)}, then V_total = V_piece × n, and V_waste = V_total × (1 + waste%).
Scope: Volume only. Sizing for soil bearing, load balancing, eccentricity, and reinforcement must be done by your engineer.

References

Waste allowance ~4–10% typical in practice (NRMCA Concrete In Practice CIP 8, CIP 31).
US bag yields: QUIKRETE® Concrete Mix 1101 data sheet.

FAQs

When should I use a trapezoidal combined footing?

Trapezoidal plans are often used to balance bearing pressure when columns carry different loads or sit near a property line. This tool only estimates volume; sizing must follow your engineer’s design.

Does this include the connecting strap or tie beam?

No. If your design includes a strap or tie beam, calculate its volume separately using the beam calculator.

Can I add more than two pedestals?

This version supports two columns (A and B). For three-column combined footings, I can provide a variant.