Retaining wall calculator

Every dimension must be a finite positive number: zero or negative length, height, or block size is rejected as invalid_input instead of a hollow zero. Use it free in the browser before you order, or call the API at $0.002 per successful request when estimating software needs a reproducible take-off.

How courses become wall blocks and a separate cap-unit count

A modular retaining wall is ordered as two product lines even when they share a face module: stacked face blocks that hold the grade, and cap or coping units that close the top, shed water, and give a finished seat. This calculator never treats the cap as a free extra you can ignore, and it never silently folds the last course into the cap SKU. There is no manufacturer SKU table, no geogrid schedule, no buried base course, and no setback batter: those are site judgements you apply after you have a clean geometric take-off. It first forms courses as the ceiling of wall_height divided by block_height, so a 1.1 m wall on 0.2 m blocks becomes six courses, not five-and-a-half. It then forms blocks_per_course as the ceiling of wall_length divided by block_length, so a 7.3 m run of 0.45 m blocks becomes seventeen pieces per row rather than a fractional 16.22 that no merchant will cut for you. wall_blocks is the product of those two integers: every course, including the top structural course, is a wall block. cap_units is a separate ceiling of wall_length divided by cap_length, because the coping stone sits on top of the finished height rather than replacing the last row. When cap_length is omitted, the engine uses block_length so a matching module still returns a distinct cap count you can buy as a different pallet. The response echoes the parsed dimensions, the exact ratios before ceiling, the integer courses and blocks_per_course, wall_blocks, cap_units, total_units as wall_blocks plus cap_units, and a short formula string for audit.

Input contract, units, defaults, and error behaviour

Keep metres with metres or feet with feet: the engine never converts units, so mixing centimetres for the block and metres for the wall would silently produce a wrong course count. Failed validation is not billed. POST a JSON body with four required fields and one optional field. wall_length is the run along the grade (aliases length, L, run, wall_run) and must be a finite strictly positive number. wall_height is the finished face height from the top of the base course to the wall top before the cap is seated (aliases height, H, wall_h) and must likewise be strictly positive. block_length is the horizontal face dimension along the wall (aliases block_width, face_length, unit_length, bl) and block_height is the course height (aliases face_height, unit_height, course_height, bh). cap_length is optional (aliases cap_unit_length, coping_length, cap_width): when you omit it, the engine copies block_length so a matching module still yields a distinct cap_units integer; when you send it, it must be a finite strictly positive number of its own. Missing fields, empty strings, non-finite values, and magnitudes above the supported ceiling fail with invalid_input naming the field. A zero or negative dimension fails with a message that the named wall_length, wall_height, block_length, block_height, or cap_length must be a positive number, matching the rule that a wall with no extent cannot consume blocks. On success the body echoes the parsed dimensions, courses_exact and courses, blocks_per_course_exact and blocks_per_course, wall_blocks, cap_units_exact and cap_units, total_units, and the formula string. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline; nothing is stored after the response returns, and the work never leaves your isolate for a model or a network hop.

Where a retaining-wall take-off with caps earns its keep

Estimators embed the contract in take-off tools so a schedule of run length, finished height, modular face size, and optional cap length becomes integer courses, wall_blocks, and cap_units without a spreadsheet full of hidden ceiling cells. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — lets you move from a phone check at the merchant to an automated pipeline without changing the mathematical result.