{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"retaining-wall-blocks"},"result":{"entity_type":"calculator","id":"retaining-wall-blocks","calculator_id":"retaining-wall-blocks","canonical_url":"https://tttkmbb.com/construction/retaining-wall-blocks","name":"Retaining Wall Block Calculator","title":"Retaining Wall Block Calculator – Blocks, Caps, Base Gravel, Drainage Backfill and Drain Pipe","category":"construction","category_name":"Construction & Home","tool_name":"estimate_retaining_wall_blocks","featured_mcp_tool":false,"description":"Estimates segmental (dry-stacked) retaining-wall blocks from the wall length and height and the block face size (courses × blocks per course plus waste), cap units for the top course, the compacted gravel base under the first course, the drainage-gravel zone behind the wall and the perforated drain pipe length. Planning estimate only.","use_when":"You need to order concrete retaining-wall blocks, caps and the gravel for the base and drainage zone of a garden or landscape wall.","do_not_use_when":"The wall is higher than about 1.2 m (4 ft), carries a slope or surcharge, or is terraced: it needs geogrid and engineering per the block manufacturer's tables. Mortared brick walls use brick; poured footings use concrete-footing.","inputs":[{"name":"wall_length","label":"Wall length","type":"number","unit":"ft or m","required":true,"max":10000,"exclusive_min":0,"description":"Length of the wall face (ft or m, see unit).","example":20},{"name":"wall_height","label":"Wall height","type":"number","unit":"ft or m","required":true,"max":100,"exclusive_min":0,"description":"Total block height including the buried first course (bury about 10 % of the height, at least 15 cm / 6 in) and excluding the caps.","example":2},{"name":"unit","label":"Length unit","type":"enum","required":false,"default":"ft","values":[{"value":"m","label":"Metres (m)","aliases":["metre","meter","metres","meters","metric"]},{"value":"ft","label":"Feet (ft)","aliases":["feet","foot","imperial"]}],"description":"Unit of the length inputs (m or ft). Lengths are reported in both units.","example":"ft"},{"name":"block_length_in","label":"Block length","type":"number","unit":"in","required":false,"default":12,"max":48,"exclusive_min":0,"description":"Face length of one block in inches (1 in = 25.4 mm); common units are 12 in and 18 in long.","example":12},{"name":"block_height_in","label":"Block height","type":"number","unit":"in","required":false,"default":4,"max":24,"exclusive_min":0,"description":"Height of one block in inches (4, 6 or 8 in).","example":4},{"name":"block_depth_in","label":"Block depth","type":"number","unit":"in","required":false,"default":8,"max":48,"exclusive_min":0,"description":"Front-to-back depth of the block in inches; the base trench is 12 in wider than this.","example":8},{"name":"cap_blocks","label":"Cap blocks","type":"boolean","required":false,"default":true,"description":"Add a course of cap units (same length as the blocks) on top of the wall.","example":true},{"name":"base_depth_in","label":"Base gravel depth","type":"number","unit":"in","required":false,"default":6,"min":0,"max":24,"description":"Compacted crushed-stone base under the first course, in inches (6 in / 15 cm is the usual minimum).","example":6},{"name":"gravel_backfill_depth_in","label":"Drainage backfill depth","type":"number","unit":"in","required":false,"default":12,"min":0,"max":48,"description":"Thickness of the clean-gravel drainage zone directly behind the blocks, in inches (12 in / 30 cm is standard).","example":12},{"name":"waste_percent","label":"Waste allowance","type":"number","unit":"%","required":false,"default":5,"min":0,"max":50,"description":"Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 5 % for straight walls; 10 % for curves and corners that need cut blocks.","example":5}],"outputs":[{"name":"courses","label":"Courses","type":"integer","decimals":4,"description":"ceil(wall_height / block_height)."},{"name":"blocks_per_course","label":"Blocks per course","type":"integer","decimals":4,"description":"ceil(wall_length / block_length)."},{"name":"blocks_before_waste","label":"Blocks (no waste)","type":"integer","decimals":4,"description":"courses × blocks_per_course."},{"name":"total_blocks","label":"Blocks to order","type":"integer","decimals":4,"description":"ceil(blocks_before_waste × (1 + waste_percent/100))."},{"name":"cap_blocks_needed","label":"Cap blocks","type":"integer","decimals":4,"description":"blocks_per_course when cap_blocks is true, otherwise 0."},{"name":"base_gravel_yd3","label":"Base gravel","type":"number","unit":"yd³","decimals":3,"description":"wall_length × (block_depth + 12 in) × base_depth."},{"name":"base_gravel_m3","label":"Base gravel","type":"number","unit":"m³","decimals":3,"description":"Base gravel in cubic metres."},{"name":"backfill_gravel_yd3","label":"Drainage backfill gravel","type":"number","unit":"yd³","decimals":3,"description":"wall_length × wall_height × gravel_backfill_depth."},{"name":"backfill_gravel_m3","label":"Drainage backfill gravel","type":"number","unit":"m³","decimals":3,"description":"Backfill gravel in cubic metres."},{"name":"gravel_total_tonnes","label":"Gravel total","type":"number","unit":"t","decimals":2,"description":"(base + backfill) × 1.6 t/m³."},{"name":"drainage_pipe_ft","label":"Drain pipe","type":"number","unit":"ft","decimals":1,"description":"Perforated pipe along the back of the base course = wall_length."},{"name":"drainage_pipe_m","label":"Drain pipe","type":"number","unit":"m","decimals":2,"description":"Drain pipe length in metres."}],"input_schema":{"type":"object","properties":{"wall_length":{"description":"Length of the wall face (ft or m, see unit). Unit: ft or m.","type":"number","maximum":10000,"exclusiveMinimum":0,"examples":[20],"x-unit":"ft or m"},"wall_height":{"description":"Total block height including the buried first course (bury about 10 % of the height, at least 15 cm / 6 in) and excluding the caps. Unit: ft or m.","type":"number","maximum":100,"exclusiveMinimum":0,"examples":[2],"x-unit":"ft or m"},"unit":{"description":"Unit of the length inputs (m or ft). Lengths are reported in both units.","type":"string","enum":["m","ft"],"default":"ft","examples":["ft"]},"block_length_in":{"description":"Face length of one block in inches (1 in = 25.4 mm); common units are 12 in and 18 in long. Unit: in.","type":"number","maximum":48,"exclusiveMinimum":0,"default":12,"examples":[12],"x-unit":"in"},"block_height_in":{"description":"Height of one block in inches (4, 6 or 8 in). Unit: in.","type":"number","maximum":24,"exclusiveMinimum":0,"default":4,"examples":[4],"x-unit":"in"},"block_depth_in":{"description":"Front-to-back depth of the block in inches; the base trench is 12 in wider than this. Unit: in.","type":"number","maximum":48,"exclusiveMinimum":0,"default":8,"examples":[8],"x-unit":"in"},"cap_blocks":{"description":"Add a course of cap units (same length as the blocks) on top of the wall.","type":"boolean","default":true,"examples":[true]},"base_depth_in":{"description":"Compacted crushed-stone base under the first course, in inches (6 in / 15 cm is the usual minimum). Unit: in.","type":"number","minimum":0,"maximum":24,"default":6,"examples":[6],"x-unit":"in"},"gravel_backfill_depth_in":{"description":"Thickness of the clean-gravel drainage zone directly behind the blocks, in inches (12 in / 30 cm is standard). Unit: in.","type":"number","minimum":0,"maximum":48,"default":12,"examples":[12],"x-unit":"in"},"waste_percent":{"description":"Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 5 % for straight walls; 10 % for curves and corners that need cut blocks. Unit: %.","type":"number","minimum":0,"maximum":50,"default":5,"examples":[5],"x-unit":"%"}},"additionalProperties":false,"required":["wall_length","wall_height"]},"output_schema":{"type":"object","properties":{"courses":{"description":"ceil(wall_height / block_height).","type":"integer"},"blocks_per_course":{"description":"ceil(wall_length / block_length).","type":"integer"},"blocks_before_waste":{"description":"courses × blocks_per_course.","type":"integer"},"total_blocks":{"description":"ceil(blocks_before_waste × (1 + waste_percent/100)).","type":"integer"},"cap_blocks_needed":{"description":"blocks_per_course when cap_blocks is true, otherwise 0.","type":"integer"},"base_gravel_yd3":{"description":"wall_length × (block_depth + 12 in) × base_depth. Unit: yd³.","type":"number","x-unit":"yd³"},"base_gravel_m3":{"description":"Base gravel in cubic metres. Unit: m³.","type":"number","x-unit":"m³"},"backfill_gravel_yd3":{"description":"wall_length × wall_height × gravel_backfill_depth. Unit: yd³.","type":"number","x-unit":"yd³"},"backfill_gravel_m3":{"description":"Backfill gravel in cubic metres. Unit: m³.","type":"number","x-unit":"m³"},"gravel_total_tonnes":{"description":"(base + backfill) × 1.6 t/m³. Unit: t.","type":"number","x-unit":"t"},"drainage_pipe_ft":{"description":"Perforated pipe along the back of the base course = wall_length. Unit: ft.","type":"number","x-unit":"ft"},"drainage_pipe_m":{"description":"Drain pipe length in metres. Unit: m.","type":"number","x-unit":"m"}}},"formula":"courses = ceil(wall_height / block_height); blocks_per_course = ceil(wall_length / block_length); total_blocks = ceil(courses × blocks_per_course × (1 + waste/100)); caps = blocks_per_course; base_gravel = wall_length × (block_depth + 12 in) × base_depth; backfill_gravel = wall_length × wall_height × backfill_depth; tonnes = m³ × 1.6; drain_pipe = wall_length.","method":"Follows the usual segmental retaining-wall detail: a compacted crushed-stone base 6 in deep in a trench 6 in wider than the block on each side, a perforated drain pipe at the base behind the blocks and 12 in of clean gravel backfill; gravel volumes are as-placed (loose material compacts 10–20 %). Planning estimate only; check quantities against the supplier's coverage figures and local code before ordering.","sources":[{"name":"Wikipedia – Retaining wall","url":"https://en.wikipedia.org/wiki/Retaining_wall","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Bulk density","url":"https://en.wikipedia.org/wiki/Bulk_density","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"20 ft × 2 ft wall, 12 × 4 × 8 in blocks, caps, 6 in base, 12 in backfill, 5 % waste","inputs":{"wall_length":20,"wall_height":2,"unit":"ft","block_length_in":12,"block_height_in":4,"block_depth_in":8,"cap_blocks":true,"base_depth_in":6,"gravel_backfill_depth_in":12,"waste_percent":5},"expected":{"courses":6,"blocks_per_course":20,"blocks_before_waste":120,"total_blocks":126,"cap_blocks_needed":20,"base_gravel_yd3":0.617,"base_gravel_m3":0.472,"backfill_gravel_yd3":1.481,"backfill_gravel_m3":1.133,"drainage_pipe_ft":20,"drainage_pipe_m":6.1},"url":"https://tttkmbb.com/api/v1/calculate/retaining-wall-blocks?wall_length=20&wall_height=2&unit=ft&block_length_in=12&block_height_in=4&block_depth_in=8&cap_blocks=true&base_depth_in=6&gravel_backfill_depth_in=12&waste_percent=5"},{"name":"10 m × 0.8 m wall, 12 × 4 × 8 in blocks, caps, 5 % waste","inputs":{"wall_length":10,"wall_height":0.8,"unit":"m","waste_percent":5},"expected":{"courses":8,"blocks_per_course":33,"blocks_before_waste":264,"total_blocks":278,"cap_blocks_needed":33,"base_gravel_m3":0.774,"base_gravel_yd3":1.013,"backfill_gravel_m3":2.438,"backfill_gravel_yd3":3.189,"drainage_pipe_ft":32.81},"url":"https://tttkmbb.com/api/v1/calculate/retaining-wall-blocks?wall_length=10&wall_height=0.8&unit=m&waste_percent=5"}],"faq":[{"q":"Should the first course be buried?","a":"Yes: bury about 10 % of the wall height, at least one course or 15 cm (6 in), so enter the total height including the buried course."},{"q":"Why is the base trench wider than the block?","a":"The compacted base extends about 15 cm (6 in) in front of and behind the block to spread the load and keep the base course from shifting, hence block_depth + 12 in."},{"q":"When do I need an engineer?","a":"Most block systems allow gravity walls up to about 1.2 m (4 ft) with level backfill; taller walls, slopes above the wall, driveways or terraces behind it need geogrid reinforcement designed from the manufacturer's charts or by an engineer, and many jurisdictions require a permit above 1 m."}],"tags":["retaining wall calculator","retaining wall blocks","how many blocks","wall cap blocks","gravel base","drainage gravel"],"related":[{"calculator_id":"gravel","reason":"Aggregate volume and weight for other layers."},{"calculator_id":"brick","reason":"Mortared brick wall quantities."},{"calculator_id":"concrete-footing","reason":"Concrete footing for a mortared wall."}],"links":{"html":"https://tttkmbb.com/construction/retaining-wall-blocks","markdown":"https://tttkmbb.com/construction/retaining-wall-blocks.md","json":"https://tttkmbb.com/construction/retaining-wall-blocks.json","api":"https://tttkmbb.com/api/v1/calculate/retaining-wall-blocks","schema":"https://tttkmbb.com/api/v1/calculators/retaining-wall-blocks","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:46:10Z","next_actions":[{"tool":"run_calculator","calculator_id":"retaining-wall-blocks","reason":"Run Retaining Wall Block Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/construction/retaining-wall-blocks.md"}}