Solve backwards
How long a retaining wall will my blocks build?
- 50 blocksThe example worked below
- Retaining Wall Block CalculatorEvery figure is its own
You have
How much retaining wall blocks?
Worked by the Retaining Wall Block Calculator at the settings below.
The settings it uses
- Wall Height
- 2 ft
- Block Face Width
- 18 in
- Block Face Height
- 6 in
- Cut and Breakage Allowance (%)
- 10
What it will do
34.1 sq ft of wall face
3.17 m²
One retaining wall. Enough for 17 ft of retaining wall 2 ft high.
Or several. Less than one retaining wall of the size the Retaining Wall Block Calculator opens on (19.5 ft of retaining wall 2 ft high).
Check it forwards
- Wall Length
- 17 ft
- It asks for
- 50 blocks
- You have
- 50 blocks
The Retaining Wall Block Calculator asks for 50 blocks at that size, and 51 blocks one step larger.
If you had more, or less
Around your amount
Each worked by the Retaining Wall Block Calculator at the same settings.
Half
25 blocks
17 sq ft
8.5 ft of retaining wall 2 ft high
Yours
50 blocks
34.1 sq ft
17 ft of retaining wall 2 ft high
Half as much again
75 blocks
51.1 sq ft
25.6 ft of retaining wall 2 ft high
Double
100 blocks
68.2 sq ft
34.1 ft of retaining wall 2 ft high
Common amounts
What each amount of retaining wall blocks covers
The sizes it is usually sold in, each worked by the Retaining Wall Block Calculator at the settings above.
| You have | It covers | As one retaining wall | Average retaining walls |
|---|---|---|---|
| 20 blocks | 13.6 sq ft(1.27 m²) | 6.8 ft of retaining wall 2 ft high | under 1 |
| 50 blocks | 34.1 sq ft(3.17 m²) | 17 ft of retaining wall 2 ft high | under 1 |
| 100 blocks | 68.2 sq ft(6.33 m²) | 34.1 ft of retaining wall 2 ft high | 1 |
| 200 blocks | 136 sq ft(12.7 m²) | 68.2 ft of retaining wall 2 ft high | 3 |
The exposed face, not the buried course
The height is the exposed, visible wall; the buried base course below final grade is not in the count, nor the levelling pad beneath it or the cap blocks on top. So the blocks you have build the face shown here, and the buried course, pad and caps come from their own stock — keep some back for them.
Curves and steps split blocks
A straight wall between two square ends cuts few blocks. Curves, steps in the base and outside corners mean splitting blocks on site, and a split rarely yields two usable halves — the calculator carries ten per cent, which a wall like that exceeds, so give it fifteen or more and expect less wall.
Above four feet it is a design
Most jurisdictions require an engineered design above about 1.2 m (4 ft), lower with a surcharge, a slope above or water. The count says nothing about sliding or overturning; drainage stone, fabric and a pipe that daylights are what keep a wall standing, and a wall that holds water is pushed by it.
How the answer is worked
Nothing here is a second formula. The Retaining Wall Block Calculator runs forwards — a size in, a quantity out — and this page grows its own starting retaining wall in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Retaining Wall Block Calculator
runs it forwardsEstimate how many retaining wall blocks you need, based on wall face area and block face size.
Work out what to buy insteadSolve backwards
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Fence pickets, worked by the Fence Picket Calculator.
Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much wall face does 50 blocks of retaining wall blocks cover?
- At the Retaining Wall Block Calculator's own settings, 34.1 sq ft (3.17 m²) — 17 ft of retaining wall 2 ft high. Every figure follows the settings, which you can change in the calculator.
- How many retaining wall blocks do I need per foot?
- Divide the wall's face by one block's face. A common 18 by 6 inch (46 by 15 cm) block covers 0.75 square feet, so a 2 foot high wall takes about 2.7 blocks per foot of length, before the ten per cent for split blocks and corners.
- How high can a retaining wall be without an engineer?
- Commonly about 4 feet (1.2 m) of exposed height, and lower where there is a slope above the wall, a surcharge such as a driveway, or water — the local code sets the figure. Above it, a segmental wall usually needs an engineered design with geogrid reinforcement.
- Do retaining wall blocks need a buried course?
- Yes — the first course is usually buried below final grade on a compacted levelling pad, which the block count here leaves out because it counts the exposed face. Add the buried course and any cap blocks to the order separately.