How to extract a bill of quantities from AutoCAD (DWG) drawings

Work on a copy, never the issued drawing, and clean it before you measure.

• Units. Check UNITS and INSUNITS. A plan drawn in millimetres and read as metres is out by a thousand in length and a million in area.
• External references. Load everything in the XREF palette. A framing plan in an unloaded xref measures as nothing.
• Clean-up. AUDIT fixes errors, PURGE drops unused layers and blocks, and OVERKILL deletes lines drawn twice on top of each other.
• A sheet list. Plans give counts, sections give depths and levels, schedules give sizes and steel, and the general notes give cover, laps and concrete grades.

Note the method of measurement the tender names, so every line follows the same rules.

A disciplined structural drawing keeps each element type on its own layer. Use that.

• LAYISO isolates the layer of an object you pick; QSELECT selects every object of one type on one layer, such as every closed polyline on the slab layer.
• The Properties palette shows a polyline’s length and a closed shape’s area. Select several hatches and it shows their cumulative area.
• MEASUREGEOM or AREA handles the shape the drafter never closed.

Then look before you trust. Drafters put a beam on the wall layer, draw a slab edge as loose lines, or leave a column on layer 0. A one-page layer map (layer, element, unit) makes those slips visible.

Columns, footings and piles are usually blocks with a mark such as C1 or F2. COUNT (or BCOUNT from the Express Tools in older versions) counts each block, and its attributes often carry the mark and size.

Watch for exploded blocks (a column that is now four lines is no longer counted), nested blocks, and dynamic blocks whose visibility state changes what is drawn. The plan count must equal the schedule count; when it does not, you have your first query.

How you get a schedule out depends on how it was drawn.

• A real AutoCAD table: TABLEEXPORT writes it to CSV for Excel.
• Lines and text: there is nothing to export. Data Extraction pulls each text and its position, not the rows, so rebuild the rows and check them against the drawing.
• An embedded spreadsheet (OLE object): open it and copy the cells.

Then multiply: the schedule gives the size of F2, the plan how many there are, the section how deep they sit.

DATAEXTRACTION is the closest AutoCAD comes to a take-off. Pick the objects (blocks, closed polylines, hatches) and the properties (name, layer, count, length, area, attributes), and send the result to Excel. Grouped by layer and block name, that is your raw measurement: slab areas, beam and wall lengths, column and footing counts. Volumes, formwork and steel you still calculate from the schedules.

Save the settings (the .dxe file). When the next revision arrives, rerun it and compare the two sheets instead of starting over.

A slip rarely shows line by line. Ratios catch it.

• Concrete per square metre of floor, storey by storey. Typical floors should agree; the one that does not has a missing or doubled element.
• Formwork per cubic metre, by element type. The section tells you what to expect: a 200 mm slab has 5 m² of soffit per m³ (1 ÷ 0.2), and a 400 × 400 mm column has 10 m² of sides per m³ (1.6 m perimeter ÷ 0.16 m² area).
• Steel per cubic metre, by element type, against your own accepted jobs (see the rebar checking guide).
• Counts three ways: the plan, the schedule and the take-off must agree.

Every assumption on the way goes on a query list with its sheet. That list becomes your RFIs.

detumble does this for the structural set, and shows its working. It reads the DWG or DXF sheets (or a zip of either): layers, schedules and notes, including bar schedules drawn as blocks or embedded as objects. It then measures a material take-off (concrete, formwork, excavation and steel per element) from a 3D model of what is drawn, and maps it to a bill of quantities, line by line.

Each quantity links to its evidence: the sheet, the schedule row, the note and a crop of the drawing. Conflicts are kept as queries instead of being silently resolved, and nothing advances without an engineer’s acceptance at a review gate.

The scope, plainly: its output is a draft until an engineer accepts it, so run the ratio checks above on it as you would on a junior’s. It needs DWG or DXF; a PDF set cannot be taken off today. Prices are on the pricing page, the QS workflow on the quantity surveyors page.