Concrete Calculator: Strip Footing / Continuous Foundation (Trench)

Estimate concrete for continuous strip footings (trenches) along walls or perimeters. Choose a rectangular (constant width) or trapezoidal section, enter one or more footing runs, and add a waste allowance. The tool returns total volume in m³, yd³, and ft³, plus approximate bag counts. Notes, formulas, and FAQs are included for clarity.

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

Footing section

Number of footing runs

1 to 12

Use separate runs for each wall line or different sizes.

Waste allowance

Covers spillage, over-excavation, and dimensional variation.

Footing runs

#	Length m	Bottom width B₁ m	Thickness T mm	Top width B₂ m

For rectangular sections B₂ equals B₁ internally. For trapezoids, enter both.

Results

Total length

0.000 m

Net volume

0.000 m³

0.000 yd³

0.00 ft³

With waste

0.000 m³

0.000 yd³

0.00 ft³

Per-run volumes

#	Length	Section area	Volume

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

Default yields are common published figures. Edit to match your local product.

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.
Choose the footing section: rectangular (constant width) or trapezoidal (enter top width).
Enter the number of runs, then fill in each run’s length, bottom width, thickness, and (if trapezoid) top width.
Add a waste allowance. Many jobs add 4–10 percent.
Read total length, volume, and bag counts. Round up when ordering.

Formulas and assumptions

Per-run section area
- Rectangular section: A = B × T
- Trapezoidal section: A = (B₁ + B₂) × T / 2
where B, B₁, and B₂ are widths (horizontal), and T is vertical thickness. Internally, widths are converted to meters, thickness to meters, so area is m².
Per-run volume: V = A × L.
Total volume: V_total = Σ V_runs.
Waste: V_waste = V_total × (1 + waste%).
Bag counts: bags = Required volume ÷ bag yield. US yields use ft³ per bag. Metric yields are editable in m³ per bag.
Scope: This estimates concrete only, not excavation shoring, reinforcement, or code sizing.

References

Waste allowance of about 4–10% is common in practice (NRMCA CIP 8, NRMCA CIP 31).
Minimum concrete footing thickness in residential work (e.g., 2021 IRC R403.1.1 requires not less than 6 in) — always follow your local code and engineer (ICC).
US bag yields: QUIKRETE® Concrete Mix 1101 (data sheet).

FAQs

What should I enter for top width B₂?

Use the concrete width at the top of the footing (after trench side slopes). If the sides are vertical, set B₂ = B₁ and choose Rectangular.

Does this include the wall or stem above the footing?

No. Calculate the wall volume separately using a wall or beam calculator and add the two.

How accurate is the waste percentage?

Waste depends on site conditions. Industry guidance often uses about 4–10% to cover spillage and variation. Check your contractor’s preference.