Retaining Wall Block Calculator (Caps and Gravel)

Columns = ceil(wall length / block length). Rows = ceil(wall height / block height). Caps are one row. Gravel is length × height × backfill depth.

Inputs

Units

Results

Face blocks: 75
Capstones: 15
Gravel backfill: 60.00ft³

Recommended gear

Calculation method

A 20 ft × 3 ft wall of 16×8 in blocks is 15 columns × 5 rows = 75 face blocks and 15 caps, plus 60 ft³ of 12 in gravel backfill. Metric mode converts wall and block sizes; the count is the same physical wall.

Exact formula

Wall in feet, block and gravel depth in inches. No batter, no geogrid, no drainage pipe extra.

Drainage

Gravel volume is the drain zone only. Add fabric and a perforated pipe; they are not in the count.

Frequently asked questions

Are caps extra blocks?

They are counted separately because they are usually a different SKU.

Should I add waste?

Add 5–10% on the order for cuts and breakage. This count is exact rectangles.

Is 3 ft a DIY height?

Many unit systems allow short gravity walls. Above that, follow the manufacturer and local rules.

Disclaimer — no professional advice, no liability

Not a structural wall design. Height, surcharge, soils and drainage need an engineer or the block manufacturer’s table.

These calculators, pages and any related content are provided “as is” and “as available”, solely for general educational and informational purposes. They are simplified mathematical estimates, not a construction drawing, cut list or material takeoff, and they do not constitute engineering, architectural, structural, building-code or other professional advice.

Results can be wrong, incomplete or inapplicable to your lumber, moisture content, species, fasteners, climate, codes or use case. You must independently verify every figure, assume all risk, and have a licensed contractor, carpenter or structural engineer review any purchase or installation before you act on it.

To the fullest extent permitted by applicable law, the site operator, authors, contributors and affiliates disclaim all warranties, express or implied, and accept no liability for any direct, indirect, incidental, special, consequential or punitive damages, or for property damage, collapse, injury, death, business interruption or financial loss, arising out of or related to the use of, or reliance on, these tools or their outputs.

Some jurisdictions do not allow certain warranty exclusions or liability limitations, including for personal injury. In those places, our responsibility is limited to the maximum extent permitted by law. If you do not agree, do not use this site.