Concrete Retaining Wall Calculator
Find out exactly how much concrete a poured retaining wall needs — bags, cubic yards, rebar and weep hole guidance, and cost.
Above the footing or ground line.
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Per linear ft breakdown
4.00 × 80 lb bags per linear ft
Mixing time
7 h 57 m
One person, 80 bags
Rebar & drainage planner
A 20 ft long, 6 inch thick, 3 foot tall wall with a standard footing needs about 1.8 cubic yards of concrete, roughly 80 × 80 lb bags once waste is added. Work it out precisely by finding the wall’s cross-section (thickness × height), adding the footing if used, multiplying by the run length, adding 5–10% waste, then dividing by your bag’s yield – or converting to cubic yards for a ready-mix order.
Concrete needed by wall size
Figures below are per 10 ft of run, wall stem only, no footing, no waste added.
| Wall size | Cross-section | Volume / 10 ft | Cubic yards | 80 lb bags |
|---|---|---|---|---|
| 6 in thick, 2 ft tall | 1.00 sq ft | 10 cu ft | 0.37 | 17 |
| 6 in thick, 3 ft tall | 1.50 sq ft | 15 cu ft | 0.56 | 25 |
| 8 in thick, 4 ft tall | 2.67 sq ft | 26.7 cu ft | 0.99 | 45 |
| 10 in thick, 5 ft tall | 4.17 sq ft | 41.7 cu ft | 1.54 | 70 |
Add a footing’s cross-section on top of these figures if your wall uses one, which most walls over a couple of feet do.
Thickness, footing and rebar guidance
| Wall height | Typical thickness | Footing needed | Engineering |
|---|---|---|---|
| Up to 2 ft | 4-6 in | Optional | Usually not required |
| 2-4 ft | 6 in | Recommended | Often allowed without a stamp |
| 4-6 ft | 8-10 in | Required | Typically required |
| Over 6 ft | Engineered | Required | Required |
Local codes vary, so always confirm the height that triggers an engineering requirement in your area before building a tall wall.
How to calculate concrete for a retaining wall
A poured wall is a constant cross-section extruded along a length, plus an optional footing.
- Find the wall stem’s cross-section. Thickness × height, both converted from inches or feet as needed.
- Add the footing’s cross-section if used. Footing width × depth, added to the stem’s area.
- Multiply by the run length. This gives total cubic feet for the whole wall run.
- Add waste. 5–10% covers spillage and form irregularities.
- Divide by bag yield and round up, or convert to cubic yards (÷27) for a ready-mix order.
Worked example
20 ft of wall, 6 in thick, 3 ft tall, with a 12×8 in footing, using 80 lb bags:
- Wall cross-section0.5 ft × 3 ft = 1.5 sq ft
- Footing cross-section1 ft × 0.667 ft = 0.667 sq ft
- Total cross-section1.5 + 0.667 = 2.17 sq ft
- Volume (× 20 ft)43.3 cu ft
- Plus 10% waste47.7 cu ft
- Cubic yards47.7 ÷ 27 = 1.77
- Divide by bag yield47.7 ÷ 0.60 = 79.5
- Round up80 × 80 lb bags
At 6,400 lb of bagged concrete, many builders order ready-mix for a wall this size rather than hand-mixing.
Poured concrete vs concrete block wall
| Poured concrete wall | Concrete block wall | |
|---|---|---|
| Formwork | Full forms needed for the pour | No forms – blocks stack directly |
| Labor style | One coordinated pour | Modular, stop-and-start friendly |
| Finish | Smooth or textured as formed | Visible block coursing, or faced |
| Best for | Taller or engineered walls | DIY-friendly shorter walls |
| Reinforcement | Rebar cast into the pour | Rebar and grout fill in block cores |
If you’re building with block instead, our Concrete Block Fill Calculator works out the grout needed for the cores.
Building a retaining wall: a quick checklist
- Check local code and depth requirementsFrost depth, footing size and maximum unengineered height all vary by area.
- Excavate and pour the footingA footing wider than the wall spreads the load and resists overturning.
- Set forms for the wall stemBraced, plumb forms keep the wall straight and the right thickness along its length.
- Place rebarVertical and horizontal bars tie the wall and footing together against soil pressure.
- Add drainage before backfillingWeep holes or a drain pipe, plus a gravel backfill zone, relieve water pressure behind the wall.
- Cure before backfillingGive the concrete time to gain strength before loading it with retained soil.
Common mistakes
- Skipping the footingA wall without a wide enough footing can tip or slide under soil pressure over time.
- No drainage behind the wallTrapped water builds up pressure that a wall’s design usually doesn’t account for.
- Backfilling too soonLoading a wall with soil before it has cured enough risks cracking or movement.
- Underestimating height triggers for engineeringMany areas require a stamped design past a certain wall height – check before building tall.
- Skipping rebarPlain concrete resists compression well but is weak in the tension that retained soil creates.
- Ordering by total volume onlyRound bags per linear foot when working in sections, so no stretch of wall runs short.
What this calculator assumes
Adjust your result if your project differs from these.
- Bag yields of 0.60, 0.45, 0.375 and 0.30 cu ft for 80, 60, 50 and 40 lb bags
- A constant rectangular wall cross-section, no batter or taper
- A simple rectangular footing add-on, not a stepped or engineered footing shape
- Standard concrete mix, not high-strength or fiber-reinforced mixes
- Water of roughly 3 quarts per 80 lb bag
- Mixing at about 6 minutes per 80 lb bag, per person
- Rebar and weep hole spacing shown are general rules of thumb, not a stamped engineering design
- Prices are whatever you enter; they are not live market rates
Common questions
How much concrete do I need for a retaining wall?
Multiply the wall’s thickness by its height to get the cross-section area, add the footing if used, multiply by the wall’s length, add 5 to 10 percent waste, then divide by your bag’s yield. A 20 ft long, 6 in thick, 3 ft tall wall with a footing needs about 80 x 80 lb bags.
How thick should a concrete retaining wall be?
A common rule of thumb for a poured concrete wall is about 6 inches thick for walls up to around 3 feet tall, with thickness increasing for taller walls that hold back more soil pressure.
Does a retaining wall need a footing?
Most retaining walls over a couple of feet tall need a footing wider than the wall itself, to spread the load and resist overturning from soil pressure behind the wall.
Do retaining walls need rebar?
Yes, in most cases. Vertical and horizontal rebar tie the wall and footing together and help the wall resist the bending forces from retained soil, especially on taller walls.
How tall can a retaining wall be without an engineer?
Many jurisdictions allow walls up to about 3 to 4 feet without a stamped engineering design, though this varies by local code. Taller walls, or walls holding back a slope or supporting a structure, typically require engineering.
What is a weep hole and why does a retaining wall need one?
A weep hole is a small drainage opening through the base of a retaining wall that lets built-up water escape. Without drainage, water pressure behind the wall can build up and push the wall over.
Should I backfill with gravel behind a retaining wall?
Yes, a gravel backfill zone behind the wall improves drainage and reduces the hydrostatic pressure that builds up from trapped water, working together with weep holes or a drain pipe.
How much does a poured concrete retaining wall cost vs a block wall?
Poured concrete typically needs more formwork labor but fewer separate units to install, while block walls are more modular and often faster for a DIY build. Material cost varies by region and wall size.
How long does a retaining wall need to cure before backfilling?
Most guidance suggests waiting at least 7 days before backfilling against a poured wall, giving the concrete time to gain enough strength to resist the soil pressure.
How many bags of concrete for a 20 ft retaining wall?
A 20 ft long, 6 in thick, 3 ft tall wall with a standard footing needs roughly 1.8 cubic yards of concrete, about 80 x 80 lb bags including a 10 percent waste allowance.
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Concrete Retaining Wall Estimate
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Project
| Wall size | — |
| Footing | — |
| Length | — |
| Waste allowance | — |
Per linear ft
| Concrete per ft | — |
| 80 lb bags per ft | — |
Total shopping list
| 80 lb bags | — |
| 60 lb bags | — |
| 40 lb bags | — |
| Water needed | — |
| Dry weight to move | — |
| Estimated cost | — |
Notes
Estimate generated by materialcalculate.com. Assumes a constant rectangular wall cross-section and standard concrete mix with yields of 0.60, 0.45, 0.375 and 0.30 cu ft for 80, 60, 50 and 40 lb bags. Confirm quantities and rebar with your engineer or supplier before buying.