Free Calculator · By SubcontractorHub Editorial Team · Published November 2026
Retaining Wall Calculator for Courses and Blocks
A retaining wall calculator on this page counts blocks from length, height, and the face you type. A 20 foot run, 4 feet high, on a nominal 8 by 16 inch face is 15 blocks per course and 6 courses, or 90 blocks. A cap course and a base volume are optional. There is no price and no geogrid.
Built by SubcontractorHub — the software contractors use to quote, finance, and run every job.
Book a DemoHow the Retaining Wall Calculator Counts
Courses from height. Blocks per course from length. Cap and base only if you ask.
Eight by sixteen inches is the nominal face from the CMHA fetch. Specified size is typically 3/8 inch less. Base starts at zero. There is no price.
15.000 blocks per course and 6.000 courses. Field blocks: 90.000. Cap course is off. Total 90.000. Whole blocks, rounded up: 90. Base volume stays blank until width and depth are both above zero.
All calculations are estimates based on historical information and should be verified by the user.
Important: nominal face, not a wall design
All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.
This Retaining Wall Calculator Uses the Nominal Face
The CMHA note on concrete masonry unit shapes, fetched again on November 6, 2026, says units typically have a nominal face 8 inches high by 16 inches long. Nominal is the module. Specified dimensions are typically 3/8 inch less, and the figure for a nominal 8 by 8 by 16 shows 7 5/8 and 15 5/8. This retaining wall calculator starts on the nominal face so the count matches the module. Type 7.625 and 15.625 if you are dividing the bare unit and you have already decided the joint is not in the count.
Openings, mortar bags, and grout live on the concrete block calculator. Use that page when the wall is a general masonry count. Use this page when the question is courses on a retaining run, plus a cap or a base you size yourself. The two counts will match on a plain 8 by 16 wall with no opening and no waste. They are not the same form.
A concrete footing under the wall, if you are pouring one, is volume on the concrete footing calculator. This page's base line is cubic feet of a trench you dimension. It is not a footing design and it is not tons.
Worked run
Length 20 feet is 240 inches. Divided by 16 inch faces, that is 15.000 blocks in a course. Height 4 feet is 48 inches. Divided by 8 inch faces, that is 6.000 courses. Fifteen times six is 90.000 blocks. The cap box is off, so nothing is added. Turn the cap on and the same run adds another 15, because a cap here is one more course of the face you typed, not a different product. Base width and depth at zero leave cubic feet blank.
| Line | Formula | Example |
|---|---|---|
| Per course | length in inches ÷ block length | 15 |
| Courses | height in inches ÷ block height | 6 |
| Blocks | per course × courses, plus one course if cap is on | 90 |
| Base | length × width × depth, only if you type both | blank |
How should you write the block count?
- Length, height, and the face you typed, labeled nominal or specified.
- Blocks per course and the course count.
- Whether the cap course was added, and that it used the same face.
- Whole blocks only after you round up, and say that you rounded.
- Base cubic feet only if width and depth were both typed.
- A line that mortar and grout, if you need them, are on the concrete block calculator. No price.
What the Count Leaves Out
Setback, geogrid, drainage stone, and a buried course were not on the CMHA size note fetched for this page. A wall that steps back uses fewer blocks in the upper courses than a plumb count. This retaining wall calculator assumes each course is the full length. If the layout steps, count the short courses yourself and do not treat 90 as that wall.
No maximum height was fetched. A 4 foot example is an input so the division is visible. It is not a permit threshold. Corners and returns add blocks the straight-run formula does not see. Add them from the plan.
Waste is not a hidden percent. Ninety is exact on the nominal module. A broken block is an extra you add, not a factor this page invented. Price stays off the sheet. The supplier ticket is the price.
Frequently Asked Questions
How does the retaining wall calculator count blocks?
Blocks per course equal the length in inches divided by the block length. Courses equal the height in inches divided by the block height. A 20 foot wall, 4 feet high, on an 8 by 16 inch nominal face is 15 blocks per course and 6 courses, or 90 blocks. The 8 by 16 face is the nominal module from the CMHA fetch, and you can type a different face.
Is this the concrete block calculator?
The concrete block calculator counts a wall on the same nominal 8 by 16 face and has boxes for openings, mortar, and grout. This retaining wall calculator counts courses, an optional extra cap course, and an optional base volume from a width and depth you type. It does not fill those mortar boxes.
What is the cap course?
If you check it, the calculator adds one more course of the same face you typed. That is geometry. It is not a cap unit from a catalog. Leave it off if the wall height you typed already includes the top course.
Does the base line include gravel tons?
No. Base volume is length times the width you type times the depth you type, in cubic feet. No unit weight was applied, because no base density was fetched for this page. Zero width or zero depth leaves the base blank.
Count the Courses Before You Price the Wall
Ninety blocks is a module. It is not a bid.
Get a Free DemoAll calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.