Concrete Retaining Wall Calculator

1. Enter the wall length and the stem height in feet.
2. Enter the stem thickness in inches.
3. Enter the base width and base thickness in inches for the footing under the stem.
4. Set a 10 percent waste allowance and a bag size, then read the cubic yards to order.

Here is what each result line means:

A concrete retaining wall calculator turns the size of a poured retaining wall into the amount of concrete to order. It is built for the common cantilever wall: an upright stem sitting on a wider base footing, the two forming an inverted T or L in section.

Unlike a plain wall, a retaining wall depends on its base to resist the soil pushing on it, so the base is a large share of the concrete. The tool adds the stem and the base, converts to cubic yards and bags and adds waste. To get the mix right use the concrete mix calculator, and for the binder the cement calculator.

A cantilever wall is two rectangles in section: the stem, which is the wall height times its thickness, and the base, which is the footing width times its thickness. Each runs the full length, so the volume is that section area times the length.

1. Convert the stem thickness, base width and base thickness from inches to feet by dividing by 12.
2. Multiply the length by the stem height by the stem thickness for the stem volume.
3. Multiply the length by the base width by the base thickness for the base volume, and add the two.
4. Add the waste allowance, divide by 27 for cubic yards and by the bag yield for a bag count.

For the placed weight on the ground, the concrete weight calculator gives the tonnage.

Suppose you are pouring a 30 foot garden wall with a 4 foot stem 8 inches thick, on a base 36 inches wide and 12 inches thick, at 10 percent waste.

Calculation: the stem is 30 x 4 x 0.667 = 80 cu ft and the base is 30 x 3 x 1 = 90 cu ft, so the wall is 170 cu ft, or 6.30 cubic yards. Adding 10 percent waste gives 187 cu ft, about 6.93 cu yd, of which the base is more than half.

The lesson: the base often holds more concrete than the visible stem, which is why sizing only the wall face badly under-orders a retaining wall.

Stem Height

A taller wall needs a taller stem and, by design, a wider and thicker base, so the concrete rises faster than the height alone suggests.

Base Width

The base resists overturning and sliding, so it grows with the height retained. It is often the largest single part of the pour.

Stem Thickness and Taper

A thicker stem adds volume along the whole length. A stem that tapers is thinner at the top; using the base thickness throughout gives a safe, slightly high estimate.

Keys and Over-dig

A shear key below the base, or a base trench dug wider than the form, adds concrete. Add a key separately and keep a waste margin for over-dig.

Retaining walls can be poured concrete or built from block, and the two are estimated differently.

For a block wall, count the units instead; for the delivered price of a poured wall, the concrete cost calculator in the related tools prices it by the yard.

Ordering Concrete for a Wall

Size the base and the stem separately so you can order the base pour first and the stem lift after.

Comparing Wall Sections

Try a wider base or a thicker stem to see how much each change adds before you settle on a design with your engineer.

Budgeting a Landscape Job

The total volume and weight help you price the concrete and plan access for the truck or pump.

1. Sizing Only the Stem

The base is often more than half the concrete. Leaving it out badly under-orders the wall.

2. Mixing Up Inches and Feet

Enter the length and stem height in feet and the thicknesses and base width in inches, as the fields are labelled.

3. Forgetting a Shear Key

A key below the base adds concrete that is easy to miss. Work it out separately and add it.

4. Skipping Drainage

Water behind a wall is the usual cause of failure. Drainage gravel and weep holes are not concrete, but they are part of the job.

5. Treating the Estimate as a Design

A retaining wall is structural. Stem, base and reinforcement must come from an engineer or code, especially for walls over about 4 feet.

The arithmetic is exact for a rectangular stem on a rectangular base; the usefulness depends on the section you enter.

Add the stem volume, length times height times stem thickness, to the base volume, length times base width times base thickness, all in feet, then divide by 27 for cubic yards. A 30 foot wall with a 4 foot, 8 inch stem on a 36 by 12 inch base is 170 cubic feet, about 6.30 cubic yards before waste.

The base resists the soil pushing the wall over or sliding it, so it is wide and thick. On many walls it holds more concrete than the visible stem, which is why it must be in the estimate.

Bases are often about half to two thirds of the wall height, but the right width depends on the soil, the slope behind the wall and any surcharge. An engineer or your local code sets it; this tool turns the width you enter into volume.

Often, yes. Many jurisdictions require an engineered design and a permit for walls over about 4 feet, or for walls with a slope or load behind them. The tool flags stems over 4 feet for that reason.

Yes, and it is common to pour the base first and the stem as a second lift, tied with reinforcement. The tool shows the stem and base volumes separately so you can order each pour.

A 30 foot garden wall with a 4 foot stem is roughly 312 eighty-pound bags with waste, which is far too many to mix by hand, so most poured retaining walls are ready-mix. The tool still gives the bag count for a short low wall.

No. It estimates the concrete only. Drainage gravel, filter fabric and weep holes behind the wall are separate materials, but they are essential to a wall that lasts.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• QUIKRETE Concrete Mix 1101 data sheet (QUIKRETE; bag yields 0.60, 0.45 and 0.30 cu ft).
• American Concrete Institute (ACI; reinforced concrete and the ACI 318 design standard).
• American Cement Association (American Cement Association; concrete walls and foundations).