DWG vs PDF vs IFC: Which Format Works Best for Quantities?
DWG, PDF and IFC can all support a quantity takeoff, but they carry different information: DWG holds precise vector geometry organised in layers, PDF is a universal sheet that may be vector or a flat scan, and IFC describes building elements as objects with properties. None of the three guarantees a complete quantity on its own. In practice, the completeness of the drawing set matters more than which format it arrives in.
What does a DWG file contain for quantity takeoff?
A DWG file contains vector geometry drawn at real-world size, organised in layers, blocks and annotation, which makes it precise for measuring lengths and areas. Its weakness is that a DWG is still a drawing: lines represent elements only by convention, not by definition.
The strengths of DWG for takeoff are clear. Lengths can be measured exactly rather than scaled from paper, layers often separate structural elements from architectural content, and repeated items are frequently drawn as blocks that can be counted. Dimensions, profile labels and bar marks are usually text objects that can be read directly.
The limits are just as important. Layer naming varies from office to office and is not always respected. A dimension's text can be overridden so that the displayed value differs from the geometry. Content may sit in external references (xrefs) that are not included when only the main file is sent. Several sheets may share one file through layouts at different viewport scales, so the scale has to be read from each layout, not assumed.
What does a PDF drawing contain for quantity takeoff?
A PDF drawing contains a printed representation of a sheet, and its value for takeoff depends on whether it is a vector PDF exported from design software or a raster PDF made by scanning paper. Both are universal and easy to share, which is why PDF is the most common format in tenders.
A vector PDF preserves lines and text, so lengths can be measured accurately once the scale is calibrated, and text such as profile designations and notes can usually be read. A raster PDF is a picture: lines are pixels, text has to be recognised optically, and accuracy depends on scan resolution and alignment. In both cases, the PDF has lost the structure of the original file, so layers and blocks are no longer available.
Scale is the main risk with PDF. Illustrative example: a slab of 100 m² is drawn at 1:50, but the sheet is measured as if it were at 1:100. Every length is read at double its real value, so the area reads as 400 m². With a slab thickness of 0.2 m, the concrete volume becomes 80 m³ instead of 20 m³. Checking one known dimension on each sheet prevents this entirely.
What does an IFC model contain for quantity takeoff?
An IFC model contains building elements as classified objects, such as beams, columns, slabs, walls, footings and piles, each with geometry and properties. Because an element is defined as an object rather than a set of lines, IFC is the most structured of the three formats for quantities.
The advantage is direct access to element type, material and dimensions, and in some models to precomputed quantities. The limits depend on how the model was built and exported. Elements may be classified generically instead of by their real type, the level of detail may stop short of connections and plates, and reinforcement is often not modelled bar by bar. An IFC model is also only as current as its last export, so it can lag behind the 2D drawings that carry later revisions.
How do DWG, PDF and IFC compare for quantity takeoff?
DWG, PDF and IFC compare differently on precision, structure and completeness, and the right choice often depends on what the design team actually issues. The table summarises the general trade-offs.
| Criterion | DWG | IFC | |
|---|---|---|---|
| Geometry | Precise vectors at real size | Vector or raster, depends on how it was made | 3D objects with defined geometry |
| Element meaning | By convention (layers, blocks, labels) | By reading the sheet | Explicit element classes and properties |
| Scale risk | Layouts and viewports must be read correctly | High: must be verified on every sheet | Low: model is at real size |
| Typical gaps | Missing xrefs, overridden dimensions | Scans, unreadable text, missing sheets | Generic classification, rebar not modelled |
| Rebar information | Reinforcement drawings and schedules | Reinforcement drawings and schedules | Often absent; check before relying on it |
| Availability | Common on request | Almost always available | Increasingly common, not universal |
Why does a complete drawing set matter more than the format?
A complete drawing set matters more than the format because the information needed for one quantity is usually spread across several sheets. A plan shows where an element is, a section shows its depth, a typical detail shows its reinforcement or connection, and a note may change all three.
Illustrative example: a plan shows a 100 m² slab but gives no thickness. The thickness, 0.25 m, appears only in a section. With the section, the slab is 25 m³ of concrete. Without it, any figure is an assumption, and a takeoff that guesses 0.2 m would report 20 m³ instead. This kind of silent gap is the subject of the hidden assumptions behind bill of quantities errors, and the volume formulas for every element type are in how to calculate concrete quantities.
For this reason, Quantap recommends uploading a complete set, including plans, sections, elevations and typical details, and accepts the whole set as a ZIP file. Quantap reads DWG, PDF and IFC, and when something is still unclear, missing or contradictory across the sheets, it asks through Quick Check rather than guessing.
How should you prepare drawing files for a quantity takeoff?
Drawing files should be prepared for a quantity takeoff by collecting the full, current set in the most structured format available and checking it before measuring begins. A short preparation routine avoids most format-related errors.
- Request the native formats. Ask for DWG and, where available, IFC alongside the PDF set. Use the PDF as the reference for what was formally issued.
- Collect the whole set. Include plans, sections, elevations, typical details, schedules and general notes, not only the sheets that look relevant.
- Include external references. For DWG, make sure xrefs are bound or sent with the main files, so no content is missing.
- Check revisions. Confirm every file matches the current drawing register and remove superseded sheets.
- Verify scale. On every PDF sheet, check one known dimension against the stated scale before taking any measurement.
- Package the set together. Keep related files in one folder or one ZIP so that cross-references between sheets can be followed.
For how different takeoff tools handle these formats, see the comparison of bill of quantities software. Further practical questions are answered in the FAQ.
Summary
DWG offers precise vector geometry, PDF offers universal availability with a real scale risk, and IFC offers structured element data that may still lack reinforcement and connections. Each format can support a reliable quantity takeoff when its limits are understood. The decisive factor is a complete, current drawing set in which every element can be measured from its proper source. Preparing that set carefully, and resolving gaps instead of assuming them, does more for accuracy than the choice of format.
Frequently asked questions
Can quantities be taken from a scanned PDF?
Quantities can be taken from a scanned PDF, but a scan is only an image of the sheet, so lengths depend on the scan quality and on correct scale calibration. A vector PDF exported directly from the design software is far more reliable.
Does an IFC model always include reinforcement?
No. Many IFC models show the concrete elements but do not model individual reinforcing bars, so rebar quantities often still come from the 2D reinforcement drawings and bar schedules.
Why upload a whole drawing set instead of one sheet?
A single sheet rarely carries all the information needed for a quantity. Thicknesses, profiles and reinforcement are often shown on sections, details and schedules, so a complete set lets every element be measured from the right source.
