Retaining Wall Calculator
Estimate concrete for a tapered or uniform retaining wall from top width, bottom width, height, and length.
Content updated September 14, 2026
Models a tapered (battered) or uniform wall cross-section extruded along a straight length only — no footing, drainage gravel, geogrid reinforcement, or curved runs. Wall thickness, batter, drainage, and footing sizing are structural and code decisions driven by soil and retained height — verify with a qualified professional.
Estimate the concrete volume for a retaining wall from its top width, bottom width, height, and length. Many retaining walls are battered — thicker at the base than the top — so this uses a trapezoidal cross-section rather than a single uniform thickness.
A uniform (non-tapered) wall is simply the case where top and bottom width are entered as equal values; the trapezoid formula already handles that without any special-casing.
The Retaining Wall formula
Cross-section area = ((top width + bottom width) ÷ 2) × height · net volume = cross-section area × wall length · order volume = net volume × (1 + allowance% ÷ 100)Top width and bottom width share one unit; height and wall length each use their own unit and are converted before multiplication · 1 yd³ = 27 ft³ exactly.
Worked example
An 8 in top width, 16 in bottom width, 4 ft high wall run 50 ft has a cross-section of 4 ft² and a net volume of 200 ft³. With a 10% allowance the order volume is 220 ft³ (8.148 yd³) — about 1.630 yd³ per 10 linear feet; at 0.6 ft³ per bag that is 366.667 bags, rounding up to 367.
Assumptions, rounding, and limitations
Assumptions
- The wall stem is a uniform trapezoidal cross-section (or rectangular, if top and bottom width are equal) extruded along a straight length.
- Top width, bottom width, and height are constant along the full wall length.
- The entered contingency percentage is applied directly to net volume.
Rounding: Volume math retains floating-point precision. Displayed volumes show up to three decimal places; the purchase-oriented bag result always rounds the exact quotient upward to a whole bag.
Limitations
- Does not model a footing, drainage gravel, geogrid or soil reinforcement, curved or stepped runs, or corners.
- Does not determine wall thickness, batter, or footing sizing — those depend on retained soil height and type, and are structural and local-code decisions.
- The result is a planning estimate and should be checked against approved drawings and field measurements.
Sources
- CIP 31 — Ordering Ready Mixed Concrete — National Ready Mixed Concrete Association
- NIST Guide to the SI, Appendix B: Conversion Factors — National Institute of Standards and Technology
A trapezoidal cross-section, extruded along a length
Cross-section area equals the average of top and bottom width, multiplied by height — the standard trapezoid-area formula. That area is then multiplied by the wall's total length to get volume, the same cross-section-times-length model the footing calculator uses, but with a trapezoid instead of a rectangle.
The result also reports cubic yards per 10 linear feet, a normalized rate useful for pricing or comparing wall runs of different lengths using the same cross-section.
What this does and does not model
This models the wall stem only — a straight run at a constant batter. It does not include a footing, drainage gravel, geogrid or soil reinforcement, or a curved or stepped wall run.
Frequently asked questions
▶How do I calculate concrete for a retaining wall?
Average the top and bottom width, multiply by height for the cross-section area, multiply by the wall's total length for volume, then apply your contingency allowance.
▶What does 'battered' mean?
A battered retaining wall is thicker at the base than at the top — common because the base carries more of the soil load. Enter different top and bottom widths to model it.
▶Can I use this for a uniform, non-tapered wall?
Yes — enter the same value for top width and bottom width and the trapezoid formula reduces to a simple width × height rectangle.
▶Does this include the wall's footing?
No. It models only the wall stem above the footing. Calculate a footing separately with the footing calculator and add the two volumes together.
▶Does this tell me what wall thickness or batter I need?
No. Retaining wall sizing depends on retained soil height, soil type, and drainage, and is a structural and local-code decision — verify with a qualified professional.
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Open calculator →Disclaimer: Retaining Wall Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.