Retaining Wall Calculator

How to calculate how many retaining wall blocks you need

Segmental retaining wall blocks are dry stacked in courses, which are the horizontal rows. So the count is the number of courses times the number of blocks in each one. Work in inches and round up each step, because you cannot buy part of a block. The first course goes below grade, so it counts too.

The result also shows a check by face area. It divides the wall face by the face of one block, with no rounding. The real count is a little higher, because every course ends in a part block and you cut or lose some. If the wall steps down, add one wall section for each height and the calculator adds them. Corners, curves and stairs need extra pieces that this tool does not count.

Block sizes used by the calculator

Every maker has its own sizes. These come from the maker’s own pages and were checked in October 2026. The Versa-Lok figures are from the Versa-Lok product pages. The Pavestone ones are from its cut sheets, such as the RockWall Large sheet. The Allan Block ones are from an older printing of the AB Classic brochure, which tells you to confirm exact sizes with your dealer. If your block is not here, choose “Custom block” and type its face height and length.

The Versa-Lok caps are 3-5/8 inches tall and 14 inches wide at the face, which is the cap length the calculator fills in for Versa-Lok blocks. Versa-Lok adds that its maximum heights are for 12 inch deep units in optimum conditions, and that poor soils, extra loading or slopes lower them. Pavestone’s sheets list pieces per pallet but no maximum wall height, so ask the maker.

Example: a 20 ft wall, 3 ft high

A straight wall is 20 ft long and 3 ft high above ground. You use Versa-Lok Square Foot blocks (8 × 18 inches) with the first course embedded 1/10 of the height, which is 3.6 inches, and 14 inch caps. These are the numbers the calculator shows when you open this page.

With 10% extra the same wall is 77 blocks and 20 caps. If you are buying more than one wall section, the extra is applied to the grand total.

Base and drainage stone

Versa-Lok’s installation tips call for a leveling pad of well-compacted gravel, crushed stone or coarse sand about 6 inches thick and 24 inches wide, and for 12 inches of drainage aggregate compacted behind the units. Allan Block’s tech sheet 996, which covers building steps into a wall face, gives a 6 inch deep by 24 inch wide base trench with 6 inches of compacted granular material, and the same granular material in the block cores and 12 inches behind the blocks. In Versa-Lok’s steps the base course is backfilled with native soil, and the drainage aggregate goes behind the units above it, so the calculator multiplies the drainage zone by the height above ground. The calculator starts with those numbers and lets you change them. It does not count the stone in hollow cores, filter fabric or drain pipe. See the Versa-Lok instructions and your block maker’s guide for the full list. Turn the cubic yards into tons with the gravel calculator.

How tall can a block wall be without an engineer?

Versa-Lok’s FAQ says its walls can be built three to four feet tall without engineering or soil reinforcement. Its installation tips say walls that support heavy loads or exceed four feet in height require special soil reinforcement and often professionally designed plans, and that walls taller than 4 feet typically require a design by a qualified professional engineer. It also says to check local building codes. On the limit itself, it says: “The maximum, stable unreinforced wall height in the best conditions is 4 feet and can be lower, depending on soils, loading, slopes or terraces.” It adds: “Please consult a qualified engineer if unsure about any construction, site or soil conditions.”

The calculator shows a warning when the wall is above 4 feet, and when it is above the maximum height listed for the block you pick. It compares the total stacked height, the part above ground plus the buried course, because a wall 3.8 ft above ground with a tenth buried is 4.18 ft. Rules measure walls in different ways. As one local example, the amended 2018 residential code of Bullhead City, Arizona (Section R105.2, checked October 2026) exempts from a permit retaining walls outside the setback areas that are not over 4 feet “measured from the bottom of the footing to the top of the wall,” unless they support a surcharge. That is one city’s rule. Ask your own building department. A taller wall is not something to build from a block count.

Blocks for common wall sizes

Whole blocks for a straight wall with Versa-Lok Square Foot blocks (8 × 18 inches), no buried course and no extra. Blocks for Versa-Lok Standard (6 × 16 inches) are in the second table.

Tips for ordering

• Confirm the block size with your dealer. The sizes on this page come from the makers’ own pages, but regions and producers can differ.
• Enter each step of a stepped wall as its own wall section so the courses are counted at the right height.
• Use the extra box for the allowance your supplier or contractor recommends. It raises blocks and caps together.
• Prices change by block, region and delivery, so this calculator shows none. Ask for a quote on the pieces it counts.
• Versa-Lok says walls that support heavy loads or exceed four feet in height often need professionally designed plans, and to consult a qualified engineer if unsure about any construction, site or soil conditions. Count the buried course when you measure the height, and check your local building code.

Frequently asked questions