Retaining Wall Brick Calculator

It’s easy enough to calculate units of any retaining wall, but here’s how to know which figures go into that simple calculator so the structure doesn’t topple over onto your plants. What lies behind and beneath the bricks, the wall’s base… Is often where lasting strength lie or falls short; generally it isn’t in the bricks.

First, think about the base. It must be solid. The first thing you should of do is put down a compacted layer of gravel beneath all those bricks. No matter what we do, the soil will move as it freezes, thaws, or gets soaked in a deluge. Your wall will be out of whack if there is nothing solid underneath it.

How to Calculate Your Retaining Wall Materials

Once you know the depth (typically 6 inches compacted) and the width, then use this calculator above to determine the amount of base materials you’ll need (so you don’t waste money by buying too many bags). For most walls at home, this means a 6 inch compacted layer; just enough to stabilize things but not so thick that you need industrial grade compaction machines to do it right. Skimp on this bit and even the most expensive bricks won’t spare you a wobbly wall face.

Any vertical barrier create water pressure behind it, pressure that can bend or even crack a masonry surface. To avoid that buildup, you want some kind of column of free-draining material behind the wall so that water has an exit point rather than building up at the back of the bricks. This is why we have two types of gravel: the base gravel that holds up weight and the drainage gravel that deals with hydrostatic pressure. If those two areas is separate in your calculation, you won’t end up overbuying one type and underbuying the other (which will save you money on bigger jobs).

The math shifts dramatically based off which kind of brick you buy: big concrete landscape blocks takes fewer pieces/square foot than little clay modular ones do, but then again you can bend the latter into all kinds of shapes and turn tighter corners. Big segmental blocks (like these) will shrink that number further but also be harder to set properly and need bigger setting gear. The calculator comes with reference tables that show you how depth and face length impact your overall piece-count.

For instance, a 12-inch face brick halves your labor hours compared to an eight-inch one. An eight-inch one… but also restricts your pattern-design options if you want to make tight turns. It’s a purely aesthetic/practical tradeoff; no wrong decision here, just varying results for your timeline.

Consider waste. If you’re trimming the unit to fit odd ends or a curve, your retail estimate won’t be accurate anymore. Straight walls can get away with adding about 10% waste, but curved runs often need fifteen percent or more. This accounts for wasted material when trimming for a curve or cutting corners. The calculator adds this automatically based on your input so you don’t run out of material on the last course. Running out of caps mid-project can be a time delay/extra delivery fee headache you didn’t realy want to deal with.

The deeper you bury the lower courses, the less force they will be subject to as that wall tries to topple over. Not only does this change how the wall looks, it changes its leveraged effect. For example, a one-foot-high edge will behave very differently than a three-foot-high wall. It’s also important to consider the setback angle. As each layer leans back into the hill, a little bit, this helps stabilize the wall, by way of geometry, not just because of the sheer mass of all those stones.

That batter is slight, maybe inches-per-foot-of-height or even less and yet it’s what allows a dry-stack wall to stand up without mortar.

One last thing… Be aware of local restrictions on tall stuff. Building codes requires permits and engineering stamps for walls greater than 4′ in height. While the calculator will approximate material needs, it won’t bypass your municipality’s rules. Begin with the math, confirm the law, and get digging.