10 Tips for Calculating Retaining Wall Blocks: A Beginner’s Guide

Tip 1: Block Count Depends on More Than Just a Straight Length Times Height

Wall length, wall height, and your specific block dimensions all combine to set your total block count, and corners or curved sections add complexity beyond what a simple straight-wall calculation covers. Entering every dimension accurately, not just the overall length, is what keeps the total realistic.

Tip 2: Block Size Changes Both Count and Total Weight

Standard blocks at 12 inches wide by 4 inches tall need more blocks per course than large 17-by-6 or jumbo 18-by-8 blocks, but larger blocks weigh significantly more each and change the finished look of the wall. Pick a block size based on the wall’s height and the look you want, not just to minimize block count.

Tip 3: Measure Wall Height in Inches, Not Feet

This calculator works in inches for wall height, and a measurement error here compounds across every course of the wall, not just the total. Double-check your unit before entering it, since a wall height mistakenly entered in feet instead of inches throws off the entire course count.

Tip 4: Courses Include a Buried Base Course You Won’t See When It’s Finished

A portion of most retaining walls sits below grade as a buried base course for stability, and that course counts toward your total blocks and gravel even though it’s invisible once backfilled. Don’t subtract it from your material total just because it won’t show.

Tip 5: Corners and Curves Use Blocks Differently Than a Straight Run

Enter your number of corners and any curved section length separately from your straight wall length, since both use block differently than a simple straight course. Leaving them out, or lumping them into the straight-length total, understates how many blocks the wall actually needs.

Tip 6: Base Gravel Is What Your Whole Wall Sits On

A compacted gravel base beneath the first course keeps the wall stable and level, and it’s a separate material line item from the wall blocks themselves. Skimping on base gravel is one of the more common reasons a retaining wall shifts or settles unevenly over time.

Tip 7: Drain Gravel Behind the Wall Manages Water Pressure

Retaining walls fail more often from trapped water pressure building up behind them than from the blocks themselves failing, which is why drain gravel behind the wall matters as much as the blocks in front. Don’t skip this line item to save on material cost.

Tip 8: Cap Blocks Are Optional, But They Need Their Own Adhesive

Including cap blocks gives the wall a finished top edge and adds its own quantity to your order, along with cap adhesive, sold in small tubes, to secure them in place. Skipping caps is a valid choice for a more utilitarian wall, but if you want the finished look, budget for both the caps and the adhesive.

Tip 9: Avoid the Mistakes That Lead to an Unstable Wall

Common errors include entering wall height in feet instead of inches, forgetting the buried base course in your total, skipping drain gravel behind the wall, and not counting corners or curved sections separately from the straight run. Any one of these can leave you short on material or, worse, with a wall that doesn’t perform structurally.

Tip 10: A Correctly Built Retaining Wall Is Structural, Not Just Decorative

A retaining wall with the right base preparation, drainage, and block count holds back soil pressure reliably for years, while one built without proper base or drainage is prone to bowing, shifting, or failing over time. Getting the material list right at the planning stage is what supports getting the build itself right.

Where to Go From Here

Now that you understand how block size, wall height, corners, curves, base gravel, and drainage all factor into your material list, use our Retaining Wall Block Calculator above to get an accurate count for your project. You’ll know exactly what to enter because you understand why each factor matters.