Retaining Wall Calculator

Calculate your retaining wall volume

How the calculation works

Footing volume = length × footing width × footing thickness. Stem volume = length × stem thickness × stem height above the footing. Total = footing + stem, divided by 27 for cubic yards. The two parts do not overlap, because the stem height is measured from the top of the footing. Bag counts use QUIKRETE published yields: 80 lb = 0.60 cu ft, 60 lb = 0.45 cu ft, 50 lb = 0.375 cu ft, 40 lb = 0.30 cu ft.

Worked example: 20 ft long, stem 3 ft above the footing, footing 24 × 12 in, stem 8 in → footing 40 cu ft + stem 40 cu ft = 80 cu ft = 2.96 cubic yards net (3.26 with 10% waste). Total height from the bottom of the footing is 4 ft, so the safety warnings on this page apply in full. Bags from the order volume: 147 × 80 lb, 196 × 60 lb, 235 × 50 lb, 294 × 40 lb.

Before you build: height, surcharge and local code

The 4 ft threshold is measured from the bottom of the footing. The model codes (IBC §105.2 / IRC §105.2) exempt from a permit only retaining walls “not over four feet in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge.” That is commonly misread as 4 ft of exposed wall. The two heights differ: retained height runs from the bottom of the footing to the ground at the top of the wall, while exposed height runs only from the ground at the bottom of the wall to the ground at the top. A typical footing is at least 12 in thick, so a 4 ft retained height can mean only 3 ft of exposed wall.

Engineering is triggered sooner than the permit line. Under IRC R404.4, as applied in municipal plan-review checklists, a licensed engineer's signed and sealed design is required where the wall retains more than 48 inches of unbalanced backfill, lacks permanent lateral support at both top and bottom, supports a surcharge such as a driveway, structure or sloping backfill, or is subject to hydrostatic pressure from groundwater — and walls over 24 inches that resist lateral loads in addition to soil must also be designed in accordance with accepted engineering practice. A wall can therefore need engineering even when it is under 4 ft tall. University extension guidance agrees in plain terms: walls higher than four feet often need an engineer to assess the situation so the wall can resist failure.

Local rules vary — the 4 ft line is not universal. Some jurisdictions use a lower threshold or a different measuring point: one city's handout, for example, exempts no wall more than 36 inches above finished grade, and requires a permit for walls with a surcharge over 2 ft. Editions and local amendments vary. A permit exemption is not permission to build unsafely, and it is not a finding that the wall is adequate. Check with your local building department and a licensed engineer before building.

Drainage

Every retaining wall must be properly drained. The published manufacturer and municipal guidance used on this page is: a free-draining gravel or crushed-rock zone directly behind the wall, at least 12 in deep; a 4 in perforated or slotted drain pipe at the lowest elevation within that gravel zone, with its holes or slots facing down, sloped to daylight or an approved drainage system — never a dead end; pipe outlets at manufacturer-recommended spacings (outlets at 50 ft centres with a minimum 1% pipe gradient, or at least every 40–50 ft at low points, depending on the system); and surface water graded away from the top and the toe of the wall, with no ponding above or at the toe. Drainage design is site-specific and set by the design engineer for the water conditions on the site. Where the design provides weep holes or through-wall outlets, they must discharge to a safe outlet and be kept clear — size, spacing and location are set by the engineered design and local code, and no figure is published here.

Scope: poured concrete walls only

This calculator covers poured-concrete walls only — a reinforced concrete footing plus a concrete stem, with a uniform stem thickness. It does not cover dry-stacked segmental block walls, which are built on a compacted aggregate leveling pad (not a poured footing), use manufactured block units and, where required, geogrid reinforcement, and need block counts, aggregate and geogrid quantities instead of footing and stem concrete volume. Do not use this calculator for a segmental wall. Tapered stems, stepped or tiered walls, footing keys, counterforts and curved walls are also out of scope — no verified volume method for them is used on this page.

How to use this calculator

1. Enter your measurements in the calculator above, in the units shown.
2. Check the inputs against what you measured — depth is the number most often entered wrong.
3. Press Calculate, then use the order amount (with waste, where shown) when you buy or order.

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