Free Calculator Tool
Retaining Wall Height & Footing Calculator
Calculate your wall's true retained height, check the permit threshold for your state, estimate footing dimensions, and find out whether engineering is required — all in one tool.
The retained height calculation and permit threshold comparison give you a clear picture of whether a permit is likely required. The footing estimates are rule-of-thumb starting points — actual footing dimensions must be specified by a licensed structural engineer for permitted walls. Use these numbers to have an informed conversation with your building department and your engineer.
Understanding the Calculations
Why Retained Height Differs from Visible Height
Building codes measure from the bottom of the footing — the buried base of the wall — to the top of the wall. This accounts for the full depth of soil that the wall is holding back. A standard concrete block footing is typically 12–18 inches deep, meaning nearly every wall is taller (from a permit perspective) than it appears above grade. This calculator adds your footing depth to your visible wall height to produce the retained height that inspectors actually measure.
Footing Width Rule of Thumb
A standard footing for a concrete masonry unit (CMU) retaining wall is typically 2 to 3 times the wall thickness in width, and at least 12 inches deep (or below the frost line if that is deeper). For a standard 8-inch CMU wall, the footing is typically 16–24 inches wide. These estimates scale up for taller walls because overturning moment increases with wall height squared — doubling the wall height roughly quadruples the footing size requirement in clay soils. Your engineer will calculate the precise footing size based on your soil bearing capacity, frost depth, and surcharge conditions.
The Tiered Spacing Rule
Two walls are treated as a tiered system when horizontal spacing < 3 × lower wall height (IRC R404.4). When tiered, the combined retained height of both walls is used for permit threshold determination — not each wall individually.
Why Footing Depth Changes the Permit Answer
The single most common mistake homeowners make when self-assessing a retaining wall is measuring only the visible portion above grade. Building departments measure retained height from the bottom of the footing — which is buried — to the top of the wall. Because a standard footing is 12 to 18 inches deep, a wall that looks like it's comfortably under a 4-foot threshold by eye can actually be at or above that threshold once the footing is included. This calculator exists specifically to catch that gap before it becomes a surprise during a permit application or, worse, after construction is already complete.
How the Footing Width Estimates Are Derived
The footing width figures in the table above follow a simplified version of the relationship structural engineers use: footing size needs to grow faster than wall height because the overturning force on a retaining wall increases with the square of its height, not linearly. A wall twice as tall doesn't need a footing twice as wide — it typically needs one three to four times larger, depending on soil bearing capacity. These figures are conservative starting estimates for typical soil conditions and are not a substitute for an engineer's calculation on any wall that requires one.
Frequently Asked Questions
No. The footing dimensions shown here are rule-of-thumb estimates for planning purposes only. Any wall that requires a building permit with footing details will need those dimensions specified by a licensed structural engineer based on your actual soil conditions, surcharge loads, and local frost depth — not from a generalized online calculator.
When two walls are spaced closer than three times the lower wall's height, building codes treat them as a single combined structure for permit purposes. Adding the second wall's height lets this calculator show you the combined retained height that your building department will actually evaluate, rather than just the height of the one wall you're focused on. See our full explanation in the tiered wall guide.
Use your local frost depth as a starting estimate — footings are generally required to extend below the frost line in your area. Frost depths range from near 0 inches in parts of the Gulf Coast and Southern Florida to 48 inches or more in the upper Midwest and northern New England. Your local building department can tell you the exact frost depth requirement used in your jurisdiction.