Estimate Continuous Footing & Trench Concrete
Use the Concrete Strip Calculator to estimate cubic feet, cubic yards, concrete bags and material cost for continuous strip footings, wall foundations, trench pours and multiple footing runs.
Choose one strip geometry below, enter the finished concrete dimensions and calculate the quantity to plan.
Best for one strip footing, foundation run, grade trench or narrow continuous pour with a constant cross-section.
Material estimate only; not a footing design or code-compliance calculation.
Add several wall or footing runs that use the same strip width and depth.
Material estimate only; verify drawings and field dimensions.
Calculate up to three strip sections separately when length, width or depth changes.
Material estimate only; stepped footing geometry must follow the construction documents.
Estimate whole bags for a small strip footing using the actual cubic-foot yield printed on the product.
Check the actual bag label.
Rounded to whole bags. Check manufacturer yield and project suitability before purchase.
A Concrete Strip Calculator estimates the volume of concrete needed for a long, narrow rectangular pour such as a continuous strip footing beneath a wall, a trench foundation, a garden wall base, a perimeter footing or another linear concrete element. Instead of estimating only floor area, it uses three dimensions: the length of the run, the width of the concrete strip and its depth. That produces a cubic volume, which can then be converted into cubic yards for ready-mix ordering or divided by product yield for bagged concrete.
Strip footings are common because they distribute wall loads continuously along a foundation line. The quantity calculation is simple once the required dimensions are known, but choosing those dimensions is a structural and code question. Soil bearing capacity, wall load, frost depth, footing projection, reinforcement, drainage and local construction rules may all influence the required footing. This page therefore treats the dimensions you enter as already selected by your plan, designer or applicable prescriptive requirements.
Use the straight-strip option when the entire footing has the same cross-section. Use Multiple Runs when several separate walls use the same width and depth. Use Stepped Strip when the footing changes size or elevation and can be represented as separate rectangular sections. For a small DIY footing, the bagged option converts the volume into a whole-package count.
Convert a long strip length and rectangular cross-section into cubic feet and cubic yards.
Add wall lines that share the same width and depth without doing separate calculations.
Use the product’s real cubic-foot yield to estimate whole bags for smaller jobs.
Download the calculated quantity and project details for purchasing or site notes.
When the strip is rectangular and the length is measured in feet while width and depth are measured in inches, convert both cross-section dimensions to feet before multiplying.
Cubic yards = cubic feet ÷ 27. Ordering quantity = exact volume × (1 + allowance ÷ 100).
For example, a 40-foot strip that is 16 inches wide and 8 inches deep contains about 35.56 cubic feet, or approximately 1.32 cubic yards before any allowance. Adding a 10% ordering allowance produces about 1.45 cubic yards. A supplier may require the final order to be rounded to its own increments, and small loads may be subject to short-load charges.
A common estimating error is to divide only the depth by 12 while leaving the strip width as an inch value. If length is in feet, both width and depth must be expressed in feet before multiplication. The calculator handles these unit conversions automatically, reducing a frequent source of twelve-times or 144-times errors.
A contractor may describe a footing as “80 linear feet,” but that number alone does not describe concrete quantity. Eighty linear feet of a 12 × 6 inch strip uses much less concrete than 80 linear feet of a 24 × 12 inch strip. The cross-sectional area is what turns linear footage into volume.
Confirm the required footing width, depth and any changes in section.
Add the centerline or actual concrete run lengths shown for each wall line.
Make sure shared corners are not accidentally counted twice in your length total.
Compare excavated depth and width with the intended finished concrete geometry.
Choose a realistic buffer and confirm supplier ordering increments.
If forms define the strip, measure the internal dimensions of the formwork. If concrete is placed directly against earth, the trench itself may define the final width and depth, but over-excavation can increase the actual quantity. Loose trench sides, bell-outs, soft spots and local deep areas can all consume more concrete than a perfect rectangular model predicts.
If a footing is 16 inches wide for one wall and 24 inches wide beneath a heavier section, do not average the widths unless the drawings intentionally define an equivalent shape. Calculate each segment separately and add the volumes. The Stepped Strip tool is designed for exactly that workflow.
Early estimates are useful for budgeting, but a final quantity check after excavation and before the pour can reveal conditions that the plan-based estimate missed. If the trench has grown wider because soil sloughed off, or if low spots require additional depth, update the volume before ordering.
| Project Type | Typical Geometry | Best Calculator | Key Quantity Check |
|---|---|---|---|
| Continuous wall footing | Long rectangular strip | Straight Strip | Width and depth from plans |
| Perimeter foundation | Several connected runs | Multiple Runs | Avoid double-counting corners |
| Stepped foundation | Sections vary by width/depth | Stepped Strip | Calculate each section separately |
| Garden wall footing | Narrow continuous strip | Straight or Bagged | Use local design requirements |
| Small trench pour | Concrete placed in excavation | Straight Strip | Field trench may exceed plan size |
| DIY short footing | Small rectangular volume | Bagged Concrete | Manufacturer yield per bag |
These categories describe estimating geometry rather than structural suitability. A foundation supporting a residence, retaining wall or heavily loaded structure may require engineering, while a small nonstructural garden project may be governed by simpler local requirements. Always use the dimensions that apply to your specific project.
Many foundation layouts consist of four exterior walls plus one or more interior bearing lines. When every footing uses the same width and depth, the easiest quantity method is to total the run lengths and multiply that combined length by one cross-sectional area. The Multiple Runs calculator lets you enter up to four lengths, including zero for unused rows, then performs that calculation automatically.
Be careful at intersections. If your field measurement method already includes the full outside perimeter, adding each wall dimension independently can double-count portions at corners depending on how the dimensions were taken. A clean takeoff should use one consistent convention—plan centerlines, clear runs, or explicit footing lengths—so each physical piece of concrete is represented once.
An interior footing may be wider or deeper than the exterior strip. If its section differs, do not include it in the shared-width multiple-run calculation. Put it into the Stepped Strip calculator as a separate section, or calculate it independently and add the result to the project total.
A door opening in a wall does not automatically mean the footing below it disappears. Continuous footings commonly remain continuous beneath wall openings, but the project drawings control. Estimate the concrete shown on the foundation plan rather than subtracting every architectural opening.
Sloping sites can require foundations to step vertically. Footings may also change width or depth under concentrated loads, chimneys, returns or transitions. A single average width and depth can obscure these changes, so the safer quantity approach is to split the concrete into rectangular segments that match the construction drawing.
For each segment, calculate length × width × depth, convert the result into cubic feet and then add all section volumes. Only after the sections are combined should you apply an overall ordering allowance, unless the project specifically requires different allowances for different pours.
A simple three-section calculator represents each segment as a rectangular prism. Real stepped foundations may include overlaps, keyways, thickened transitions or geometry that cannot be captured by three simple boxes. For complex work, use a detailed takeoff from the structural drawings. The calculator is best treated as a fast estimator rather than a substitute for a professional quantity survey.
The answer depends entirely on its length and cross-section. A 50-foot footing that is 12 inches wide and 6 inches deep contains 25 cubic feet, or about 0.93 cubic yard. The same 50-foot length at 24 inches wide and 12 inches deep contains 100 cubic feet, or about 3.70 cubic yards—four times as much concrete. This illustrates why a “price per linear foot” or “yards per 100 feet” shortcut can be misleading unless width and depth are fixed.
If you know the concrete volume per linear foot, you can use it as a quick check. The volume per foot equals width in feet × depth in feet. For a 16-inch × 8-inch strip, each linear foot contains about 0.889 cubic foot. Multiplying that by total run length should match the calculator’s exact cubic-foot result before allowance.
Convert 18 inches to 1.5 feet and 8 inches to 0.667 foot. Multiply 60 × 1.5 × 0.667 to get approximately 60 cubic feet. Divide by 27 to obtain about 2.22 cubic yards exact. With a 10% allowance, the planning quantity is about 2.44 cubic yards before supplier rounding.
Ready-mix delivery is often practical when a footing contains enough volume that hand mixing would create a long, labor-intensive placement.
Bagged mixes can suit short strips, isolated repairs or remote locations where ready-mix access is impractical.
Do not choose bagged concrete solely because the raw material price appears lower. Include mixer capacity, water supply, labor, placement time and the need to keep a footing placement continuous. Conversely, a very small footing may be uneconomical for a truck delivery after minimum-order charges.
To estimate bags, first calculate the ordering volume in cubic feet, including the chosen allowance. Divide that number by the published yield per bag and round up. For example, if a short strip needs 7.2 cubic feet with allowance and the selected product yields 0.60 cubic foot per bag, the estimate is 12 bags.
The bag’s nominal weight is not enough by itself. Use the yield printed on the specific concrete mix.
Different formulations, aggregate sizes and package weights can have different yields. The calculator therefore asks for yield rather than assuming that every 60 lb or 80 lb product produces the same volume. This keeps the estimator compatible with many brands and metric or specialty products once their cubic-foot equivalent is known.
A theoretical strip calculation assumes perfect dimensions. Actual excavations and forms can vary. An ordering allowance provides a planning buffer for small over-width areas, uneven trench bottoms, spillage and measurement uncertainty. The calculator allows a percentage between 0% and 50% so you can see how the buffer affects quantity.
There is no universal percentage that is correct for every footing. A precisely formed strip on a prepared base may need less contingency than an earth-formed trench in unstable soil. The purpose of an allowance is not to replace measurement. If the trench is visibly much wider than the plan, measure the actual condition instead of applying a large arbitrary percentage to an outdated estimate.
Your calculated result may be 2.44 yd³ while the supplier accepts orders only in certain increments. The quantity to purchase can therefore differ from the mathematical result. Ask how the supplier rounds, whether a minimum load applies and what happens to excess concrete. Plan a safe location for small leftovers rather than improvising after the truck arrives.
The most important limitation of any online concrete strip calculator is that it cannot design the footing. Width and depth are not selected by volume mathematics. They can depend on building loads, soil capacity, frost conditions, wall material, eccentricity, nearby excavations, reinforcement and local building requirements. Structural footings can also be governed by flexure and shear design.
The American Concrete Institute’s residential concrete guidance includes separate treatment of footing purpose, footing types, design considerations and construction, and it notes that applicable codes and construction documents take precedence over general guidance. That is a useful boundary for this calculator: use the drawings or accepted design requirements to establish the geometry, then use this page to estimate the concrete that geometry consumes.
For ordinary estimating, the volume displaced by reinforcing steel is typically small relative to the footing volume and is not deducted from the concrete quantity. Reinforcement quantity itself should be estimated separately from the bar schedule or design. Use the Concrete Rebar Calculator if your project specifies reinforcing bars and you need a separate material takeoff.
Some strip footings are poured into forms; others are poured directly into excavated trenches where permitted. The estimating implications are different. Formed work tends to provide a more controlled cross-section, while earth-formed trenches can widen as soil breaks away. Wet or loose soil can make dimensions less predictable and may require corrective preparation before concrete placement.
If the trench is intended to act as the form, take several width and depth readings along the run. A single measurement at the neatest location can understate the average volume. Where the plan requires a clean bearing surface or specific footing elevation, follow the project specification for excavation, dewatering and subgrade preparation.
The calculator assumes the entered depth represents concrete, not a mixture of concrete and loose spoil. Remove loose soil, debris and standing water as required by the construction documents and accepted site practice. If over-excavation occurs, the designer or inspector may need to determine the correct remedy rather than simply filling every void without review.
The calculator’s ready-mix cost is intentionally simple: ordering cubic yards multiplied by the price per cubic yard that you enter. This is a material estimate, not an installed footing price. It does not automatically include delivery, short-load fees, pumping, labor, excavation, forms, reinforcement, inspections, testing, curing, taxes or disposal of excess material.
For bagged concrete, estimated cost is whole bags multiplied by your entered price per bag. If the project requires many bags, compare that result with a local ready-mix quote and the labor needed to mix continuously. A cheaper material unit can become more expensive when equipment, time and crew size are included.
Linear footage is not enough. Always include the strip width and concrete depth.
Both width and depth must be converted to feet when length is entered in feet. The calculator performs this automatically.
Perimeter footings can be overstated when each wall length is added independently and overlapping corner sections are included twice. Use one consistent takeoff method.
Excavation depth from grade is not always the same as concrete footing thickness. A trench may include granular base, a stem wall or other foundation components. Enter only the actual concrete strip depth being calculated.
Continuous footings may run beneath door and window openings. Quantity should follow the foundation plan, not the architectural opening schedule alone.
An earth-formed footing may consume more concrete than the drawing’s perfect rectangle if the trench sides break away. Recheck actual dimensions before ordering.
The calculator accepts whatever geometry you enter. That does not mean the geometry is structurally adequate.
Confirm footing width, depth, steps and any thickened locations.
Use one consistent convention and avoid duplicate corners.
Look for widening, loose sides, water and local deep spots.
Place bars, dowels and supports according to the drawings.
Confirm truck, pump, buggy or wheelbarrow route before ordering.
Have protection and curing materials available before placement.
Use the main Concrete Calculator for slabs, columns and other shapes. If your strip includes reinforcing steel, use the Concrete Rebar Calculator. For general placement logistics, see the Concrete Pour Calculator, and if weather may affect placement, review the Concrete Rain Pour Calculator. Small damaged footing areas can also be estimated with the Concrete Repair Calculator.
For broader technical guidance, the American Concrete Institute’s ACI 332.1R-18 Guide to Residential Concrete Construction includes chapters addressing footings, concrete materials, placement and other residential concrete topics. Applicable codes, drawings and project specifications should control your actual foundation design.
External references support general education about footing construction and foundation systems. They do not replace the project’s adopted code, design drawings or professional advice.
Measure the continuous run length, finished strip width and concrete depth. Keep excavation depth and wall height separate unless they are actually part of the concrete strip being estimated.
Common questions about strip footing volume, cubic yards, bags, measurement and ordering.