Retaining Wall Block Calculator
Enter the wall length and the height showing above grade, then pick a block. The calculator adds buried courses below grade.
How it works
Courses above grade = exposed height ÷ block height, rounded up. Buried courses = buried share × exposed height ÷ block height, rounded up, at least one. Blocks per course = wall length ÷ block face length. Blocks = blocks per course × total courses × (1 + allowance), rounded up. Caps = wall length ÷ cap length (or VERSA-LOK's 0.86 caps per lineal ft), rounded up.
Worked example: VERSA-LOK: a 20 ft wall 3 ft high is 60 sq ft × 1.5 = 90 units (15 per course × 6 courses), plus 20 × 0.86 = 17.2, so 18 caps. With one buried course added, the calculator shows 105 units before allowance.
Assumptions
- Block presets: Allan Block lists the AB Classic as 18 in long × 8 in high (about 1 sq ft) with 18 in capstones; VERSA-LOK lists the Standard unit face as 16 × 6 in (2/3 sq ft, 1.5 units per sq ft) and estimates caps at 0.86 per lineal ft. Allan Block's own estimating chart runs about 2% higher than 1 block per sq ft.
- Buried depth default 1/10 of the exposed height: VERSA-LOK says walls usually have one-tenth of the exposed height embedded below grade (a 10 ft exposed wall has at least 1 ft buried). At least one buried course is a JobsiteCalc assumption; follow your block maker's guide.
- Straight wall on level ground. Corners, curves, steps and stepped bases change the count; Allan Block adds corner blocks for each course with a corner or step.
- The waste allowance is an editable JobsiteCalc default, not an industry standard. Ask your supplier what extra they suggest for your job.
- This is a quantity estimate only, not a wall design. Allan Block describes its gravity walls for common residential walls up to 6 ft; taller walls, slopes, driveways, structures or water near the wall need engineering and geogrid. Many places require a permit above a set height, so check local codes.
Frequently asked questions
How many retaining wall blocks do I need?
Divide the wall length by the block face length for blocks per course, then multiply by the number of courses (above and below grade). A 20 ft wall of 18 in blocks is 13.3 per course; 3 courses need 40, which Allan Block's chart rounds to 41.
How deep should a retaining wall be buried?
VERSA-LOK says segmental walls usually have about one-tenth of the exposed height buried below grade. Follow your block maker's instructions and any engineer's design.
How many caps do I need?
One per cap length along the wall. VERSA-LOK estimates 0.86 caps per lineal foot; Allan Block's chart lists 14 capstones for a 20 ft wall.
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Sources
Formulas and reference values are from these sources. Page content last updated 2026-10-19.
- Allan Block: Estimating a retaining wall (block and capstone charts)
- Allan Block: AB Collection specifications (AB Classic 18 × 8 in, about 1 sq ft; residential walls up to 6 ft)
- VERSA-LOK Standard design and installation guidelines (1.5 units per sq ft, 0.86 caps per ft, about 1/10 of exposed height buried)
- NIST Guide to the SI (SP 811), Appendix B.9: conversion factors (foot = 0.3048 m, ton, pound)