Retaining Wall Block Calculator

Segmental retaining wall blocks, cap units, drainage gravel and leveling pad stone for a wall of any length and height.

Above finished grade, not counting the cap.
Most manufacturers bury at least one course (or about 10% of the wall height) below grade.
Set to 0 if the wall has no cap units.
%
$per block
Your rate is remembered on this device.
$per cap
Your rate is remembered on this device.
Wall blocks (incl. waste)
170 blocks
Courses (incl. buried)
7 courses
Blocks per course
23 blocks
Cap units
25 caps
Drainage gravel (12 in zone behind wall)
3.8889
Leveling pad stone (6 in thick)
1.1111
Estimated block + cap cost
$1,145.00
Excludes gravel, drain pipe, fabric, adhesive and labor.
Height check
Over 24 in: if the wall also supports a surcharge (sloping backfill, driveway, parking or a building), IRC R404.4 requires an engineered design. Check the block maker’s maximum gravity-wall height.

Estimate generated with SortedSums: https://sortedsums.com/retaining-wall-block-calculator/. For informational purposes only; verify before relying on it.

Estimate only. This tool is for informational and educational purposes. Results depend on your inputs and simplifying assumptions, and are not a substitute for professional engineering, design or financial advice. Always verify with a qualified professional and applicable codes before purchasing, building or making decisions.

How it’s calculated

Blocks per course = ⌈ wall length ÷ block length ⌉ Courses = ⌈ exposed height ÷ block height ⌉ + buried courses Blocks = ⌈ per course × courses × (1 + waste%) ⌉ Caps = ⌈ ⌈ wall length ÷ cap length ⌉ × (1 + waste%) ⌉ Drainage gravel = length × 12 in × (courses × block height) Leveling pad = length × (block depth + 12 in) × 6 in

Example: a 30 ft wall, 3 ft exposed, with 16 × 6 in face blocks 12 in deep and one buried course: 30 × 12 ÷ 16 = 22.5 → 23 blocks per course; 36 ÷ 6 = 6 courses + 1 buried = 7 courses; 23 × 7 = 161 × 1.05 → 170 blocks, and 360 ÷ 16 = 22.5 → 23 caps × 1.05 = 24.15 → 25 caps. Drainage gravel: 30 × 1 × 3.5 ft = 105 ft³ (3.89 yd³). Leveling pad: 30 × 2 × 0.5 ft = 30 ft³ (1.11 yd³).

The Concrete Masonry & Hardscapes Association calls for a crushed-stone leveling pad at least 6 in thick extending 6 in in front of and behind the units, and drainage gravel at least 12 in behind the units. The International Residential Code requires an engineered design for walls retaining more than 48 in of unbalanced fill.

Frequently asked questions

How many retaining wall blocks do I need?

Divide wall length by block length for blocks per course, multiply by the number of courses including any buried course, then add about 5% for breakage and cuts.

How tall can a retaining wall be without an engineer?

The IRC requires an engineered design when a wall retains more than 48 in of unbalanced fill or exceeds 24 in while supporting other loads. Manufacturers also publish maximum gravity-wall heights for each block; local rules may be stricter.

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Sources

Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.

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