Free Retaining Wall Calculator
This free retaining wall calculator sizes a real wall, not just a block count: enter your length and height and get courses (including the buried one), block or 6×6 timber quantities, the reinforcement schedule, gravel footing and drainage volumes in cubic yards, and a complete shopping list down to the drain pipe and filter fabric. It handles both wall types we’ve built — concrete block and landscape timber — with the same footing and drainage spec, so you can compare them honestly.
Retaining Wall Calculator
Size your wall and get the full build spec: courses, reinforcement schedule, footing and drainage-stone volumes, and a complete shopping list — for timber or block.
Your wall
Your wall spec
| Item | Spec | Amount |
|---|
📩 Email me my wall spec
Get this exact build spec and shopping list for your 24 ft × 3 ft wall sent to your inbox, with the build guide — free.
Wall sizing FAQ
Why is one course buried?
The first course sits below finished grade on the compacted footing — it locks the wall in place. The calculator adds it automatically.
How tall can I go?
Check your local code first — many areas require engineering (and a permit) over 4 ft. This calculator flags reinforcement (deadmen or geogrid) per the build guides.
Affiliate links above may earn this site a small commission at no extra cost to you. Tool by Rogue Engineer — measurements match our retaining wall build guides.
What the calculator gets right that block math misses
Dividing wall area by block face is how people end up short. This calculator counts the way the wall actually stacks: courses are your height divided by course height plus one buried course that locks the wall below grade, block walls get a matching cap-block count for the top, and timber walls add roughly 5% for stagger waste, because an 8-foot timber almost never lands on an 8-foot mark. Change the block size and the totals rebuild — a 12″ block and a 16″ block disagree by hundreds of units on a long wall.
It also refuses to let the invisible parts disappear. Every wall gets a compacted crushed-gravel footing under the buried course, a washed-gravel drainage column behind it, 4″ perforated drain pipe at the base, and non-woven filter fabric between gravel and soil. Walls rarely fail from weak blocks — they fail from water that never got a way out.
Reinforcement, scheduled automatically
Past a certain height, gravity needs help, and the calculator schedules it. Block walls over about 3 feet get geogrid: layers no more than 16″ apart vertically, run back into the slope about as far as the wall is tall, with the square footage totaled on the shopping list. Timber walls over about 2 feet get deadmen: 6×6 tiebacks every third course, roughly 8 feet apart, each ending in a 2-foot cross buried in the backfill — and the timber count includes them. Below those heights, it tells you plainly that reinforcement isn’t needed.
Timber walls also get the fastening schedule: ½″ × 3-foot rebar pins anchoring the first course about every 2 feet, and 10″ structural timber screws tying each course to the one below it, converted into boxes of 50 so the list matches what the store actually sells.
How to use the retaining wall calculator
1. Enter length and height. Height is retained height — grade to the top of the wall. The calculator works to 6 feet, and flags where local codes typically demand an engineer.
2. Pick your material. Block mode asks for your block’s width and height off the pallet tag; timber mode assumes 8-foot pressure-treated 6×6s. The dig plan — trench width, footing depth, and how far to cut back the hillside — updates with the wall.
3. Email yourself the wall spec. The full spec and shopping list for your dimensions, sent free — take it to the stone yard and they’ll convert the cubic yards to tons on the spot.
Materials for common block wall sizes
Quick reference for block walls using a standard 12″ × 4″ locking block, straight from the calculator’s math (one course buried, footing trench 16″ wide with compacted gravel, ~12″ drainage column behind the wall):
| Wall (L × H) | Courses | Blocks | Caps | Geogrid | Footing gravel | Drainage gravel |
|---|---|---|---|---|---|---|
| 20 ft × 2 ft | 7 (6 above grade) | (140) | (20) | — | 0.75 yd³ | 1.5 yd³ |
| 25 ft × 3 ft | 10 (9 above grade) | (250) | (25) | — | 1 yd³ | 3 yd³ |
| 40 ft × 4 ft | 13 (12 above grade) | (520) | (40) | 3 layers | 1.5 yd³ | 6 yd³ |
Retaining wall calculator FAQ
How many blocks do I need for a retaining wall?
Blocks per course is your wall length divided by the block width; courses is your height divided by the block height, plus one buried course. The calculator does both, adds the matching cap-block count for the top, and updates the moment you change block size — a 12×4 block and a 16×6 block give very different totals for the same wall.
Why does the calculator bury a course?
The first course sits below finished grade on the compacted gravel footing. That buried course is what locks the bottom of the wall in place — skipping it is one of the most common reasons short walls lean within a few seasons. The calculator adds it automatically for both block and timber walls.
How much gravel does a retaining wall need?
Two separate volumes, and the calculator reports both: crushed ¾-inch gravel for the footing trench (compacted, under the buried course) and washed ¾-inch gravel for the drainage column behind the wall — figured at roughly a 12-inch clean-gravel backfill, with 4-inch perforated drain pipe and non-woven filter fabric on the shopping list to match.
When do I need geogrid or deadmen?
Block walls over about 3 feet get geogrid layers no more than 16 inches apart, run back about as far as the wall is tall — the calculator schedules the layers and the square footage. Timber walls over about 2 feet get deadmen: 6×6 tiebacks every third course, roughly 8 feet apart, each with a 2-foot cross at the buried end. Under those heights, it tells you reinforcement isn’t needed.
How tall a wall can this calculator handle?
Up to 6 feet of retained height — but check your local code first. Many areas require an engineer’s stamp (and a permit) over 4 feet, and the calculator flags that. Taller grades are usually better handled as two shorter terraced walls anyway.
Timber or block — which wall is cheaper?
Flip the toggle and compare your own numbers: pressure-treated 6×6 timbers usually win on material cost for short walls, while block wins on lifespan and zero maintenance. The calculator keeps the footing and drainage spec identical between the two, so the comparison is apples to apples.
From numbers to a wall that stays put
The build guides cover what the calculator can’t: the block wall, step by step — footing prep, leveling the first course, geogrid, and caps — and the landscape timber wall, from pinning the first course through deadmen and sealing cut ends. Both follow the same drainage-first philosophy this calculator budgets for.
