Retaining wall block calculator

Every line shows the quantity to buy and how StudSheet got it: the spacing, the waste and the package size, so you can check it before the supply house or the quote.

In Canada (4.88 m wall, 610 mm tall)

Set to Canada, the Sheet works the job out again for Ontario: metric sizes, bag sizes, the frost depth and the code notes. It doesn't just convert feet to meters. The first lines:

• 58 blocks, Retaining wall block: Medium block: the smallest block made for a 610 mm wall (the small block is made for up to 457 mm). 5 courses × 152 mm = 762 mm built (610 mm visible + 152 mm buried; at least 152 mm or 1/10 of the height goes below grade) × 11 blocks per course (4.88 m ÷ 445 mm) + 5% for breakage and cuts.
• 12 caps, Wall cap: 4.88 m ÷ 445 mm per cap + 5%.
• 2 tubes, Landscape block adhesive: Two beads under the caps — about 3.66 m of wall per tube.
• 39 bags (0.014 m³), Base gravel (paver base): 4.88 m × 610 mm trench × 152 mm deep, +20% because gravel compacts = 0.54 m³ loose.
• 64 bags (0.014 m³) — or 0.92 m³ delivered, Drainage stone, 19 mm clean: 305 mm zone behind the wall, from the base up to 152 mm below the top (610 mm) × 4.88 m = 0.91 m³.
• 1 roll, Landscape filter fabric: 4.5 m² between the stone and the soil, wrapped over the top.

1. Call 811 and wait for the utility markings.
2. Stake the wall line and set a string at the height of the first course.
3. Dig the trench 24″ wide × 12″ deep. Compact the bottom.
4. Add base gravel in 2–3″ layers, compacting each one, to a flat 6″ pad.
5. Set the first course on a thin screed of sand. Level every block side to side and front to back — take your time here.
6. Backfill in front of the first course. Fill 12″ behind the wall with drainage stone.
7. Stack courses with joints staggered half a block. Sweep each course clean; backfill and compact behind every course.
8. Lay filter fabric between the stone and the soil; finish the top 6″ with topsoil.
9. Glue the caps down with block adhesive.

Must-have tools first, then the ones that help and the ones to rent for the day.

Mistakes that cost a callback or a second trip

• A first course that isn’t level: Every error on course one repeats up the wall. Spend half your time on it.
• Backfilling with the dirt you dug out: Without drainage stone, water pressure pushes the wall over within a few winters.
• Skipping compaction: Loose base settles and the wall leans. Compact every 2–3″ layer.

What the calculator assumes

• Gravity wall (no geogrid). Typical block limits for total height, buried course included: small garden block ~2 ft, medium ~3 ft, large ~4 ft — check your block’s label.
• Base: 6″ of compacted gravel in a trench at least 24″ wide (Versa-Lok, Allan Block, Belgard guides); +20% loose volume for compaction.
• First course buried at least 6″ or 1/10 of the visible height, whichever is more; any rounding up to a full course goes below grade.
• 12″ of ¾″ clean drainage stone behind the wall; perforated drain pipe for poorly draining soil.
• +5% blocks for breakage and cuts.
• IRC R404.4: walls retaining more than 48″ need engineering (24″ when they carry a surcharge). New Jersey: permit at 4 ft and taller, measured from the bottom of the footing to the top of the wall, terraced walls added together (N.J.A.C. 5:23-2.14).

The Sheet sets its code notes for the job's state or province. These are New Jersey's and Ontario's; the code reference has more. Always confirm with your building department.

• Call 811 first — it’s the law: In New Jersey, call 811 (NJ One Call) at least 3 full business days before digging. Free. Wait for the utility markings.
• Permits for retaining walls: In Ontario a retaining wall more than 1.0 m tall next to public property, a building entrance or a public area is a “designated structure”: it needs a permit, drawings by a design professional (towns ask for an engineer’s stamp), and guards. Confirm with your building department.
• Click Before You Dig: Before you dig, request a free utility locate from Ontario Dig Authority (ontariodigauthority.ca) at least 5 business days ahead, and wait for the markings.

What materials do I need to build a garden or retaining wall?

For the worked example, a 16′ wall, 2′ tall, the Sheet counts 6 lines with waste included, starting with retaining wall block (58 blocks), wall cap (12 caps), landscape block adhesive (2 tubes), base gravel (paver base) (39 bags (0.5 cu ft)). Each line's math is in the table above. Put in your own sizes in the garden wall calculator and every line is counted again.

How long does it take to build a garden or retaining wall, and can I do it myself?

About 19 to 29 hours for the worked example, in 9 steps. StudSheet stamps it DIY OK: you can do this.

What tools do I need to build a garden or retaining wall?

19 in all. The must-haves start with tape measure (25 ft), mason's line + stakes, line level, 4-ft level, torpedo level, square shovel. On the Sheet you mark each one as owned, to buy or to rent.

Stuck while you build a garden or retaining wall? Ask in the Retaining and garden walls group of the StudSheet community with this Sheet attached. Homeowners who've done it and verified pros answer, and anyone can read it.

• Landscaping and hardscaping for contractors: run this takeoff at your own prices, send the estimate, and get it signed and the deposit paid.
• Concrete slab or footings (10′ × 10′ slab, 4″ thick): Bags or ready-mix yards, gravel base, rebar or mesh and forms for a slab, a pad or footings.
• Pour concrete steps (brick or stone facing optional) (3 concrete steps, 1′ 9″ rise): Forms, base, concrete (bags or a truck), rebar and the finish for a set of outdoor steps and their landing — with the frost and handrail rules where you live.
• Build a paver patio (16′ × 12′ paver patio): Excavation, compacted gravel base, 1″ of bedding sand, pavers, edge restraint and polymeric sand for a patio or walk — counted in bags or by the yard.
• All 45 Sheets, across 16 trades.
• Code reference: frost depths, guard heights, stairs, retaining walls.