Cinder Block Retaining Wall Calculator — Blocks, Rebar & Grout
Estimate blocks, vertical rebar, and grout fill for a reinforced CMU retaining wall. Consult local code for any wall over 4 ft — engineered design required.
Enter Dimensions
Recommended: 10% for standard projects
Results
Blocks Needed
199blocks
Mortar Bags
7bags
60 lb bags · 1 bag per 30 blocks (NCMA)
Wall Area
160sq ft
Blocks per Sq Ft
1.125blocks/sq ft
BIA standard for 8×16 face
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Important: a CMU retaining wall is a structural element that holds back soil and sometimes vehicle, building, or water loads. Designs of any height should be reviewed against local code; walls over 4 ft retained height almost universally require engineered drawings and a building permit. This calculator estimates materials only — it does not replace structural design.
Use this to budget block, grout, and rebar for a prescriptive or engineered wall after you've confirmed wall thickness, rebar schedule, and footing dimensions with your engineer or local building department.
How to Estimate a CMU Retaining Wall
Block count uses standard Wall Area × 1.125 × waste factor. Add to that: grout (per filled cell), rebar (vertical + horizontal), and footing concrete (separate calculation).
Materials Beyond the Block Count
- Vertical rebar: 1 piece per filled cell at specified spacing. Length = wall height + footing dowel + lap.
- Horizontal bond beam rebar: 1 #4 bar in every other course (every 16 in vertically); length = total wall length + laps.
- Grout: 8″ CMU = 0.86 cu ft per sq ft of solid-filled wall; partial grouting at 24 in OC ≈ 0.25 cu ft per sq ft.
- Footing: Separate concrete pour, typically 16″ wide × 12″ deep continuous with two longitudinal #4 bars.
- Drainage: 4″ perforated pipe per linear foot and 1 cu ft of gravel backfill per linear foot of wall.
Frequently Asked Questions
Do I need an engineer for a cinder block retaining wall?
Most U.S. jurisdictions require engineered drawings for any retaining wall over 4 ft tall (measured from bottom of footing to top of wall). Walls under 4 ft can usually be built to a prescriptive standard with code approval — but always confirm locally.
How thick should a CMU retaining wall be?
8″ CMU is the minimum for walls up to 4 ft of retained soil. 12″ CMU is required for taller walls or where surcharge loads (driveways, structures) sit above the wall. Engineered designs may specify even thicker.
What rebar do I need in a retaining wall?
Vertical #4 or #5 bars at 16–32 inches on-center extending from the footing through the top course; horizontal #4 bars in every other course (8″ vertically). All reinforced cells must be grouted solid.
How much grout fills a CMU retaining wall?
Fully grouted 8″ CMU uses ~0.86 cu ft of grout per square foot of wall face; 12″ CMU uses ~1.30 cu ft per sq ft. For partial grouting (only cells with rebar): roughly 30–50% of full-grout volume.
Do I need drainage behind a retaining wall?
Always — install a 4″ perforated drain pipe along the footing, wrapped in filter fabric, with 12 inches of clean gravel backfill. Without drainage, hydrostatic pressure can topple even a code-compliant wall.
Looking for the general calculator?
Estimate cinder blocks and mortar bags for any CMU wall. Supports 8-inch and 12-inch blocks with adjustable waste percentage and automatic pallet estimation.
Open the Cinder Block Calculator: Blocks & Mortar →