What is a DXF file — and why can't I just get a DWG?
DXF is Autodesk's open exchange format for drawings, and it is read by AutoCAD, Revit, ArchiCAD and SketchUp; DWG is Autodesk's closed format, which only their own and licensed programs can write.
Short answer: a DXF file is a drawing stored as text: every wall, door and room name is a set of lines with coordinates, grouped into named layers. DXF is Autodesk's own exchange format (Drawing Exchange Format), it is documented and open, and it is read by AutoCAD, Revit, ArchiCAD, SketchUp, Vectorworks, BricsCAD, LibreCAD and QGIS. DWG, by contrast, is Autodesk's closed binary format with no public specification — which is why ordinary apps can't write it, and why you get DXF instead. When a drawing office asks for "a DWG", what they mean in practice is "something I can keep drawing on top of" — and that is exactly what DXF is.
What actually sits inside a DXF file?
A DXF file is plain text. Open it in a text editor and you'll see pairs of code numbers and values: a code for "this is a line", a layer name, a start point and an end point. A wall running from the point (0.00, 0.00) to (4.12, 0.00) is stored as exactly those four numbers.
That has three practical consequences. First, a DXF file can be read by a program that has never heard of the app that wrote it — there is no secret structure to decode. Second, the file is small: a floor plan of an ordinary home typically runs to a few hundred kilobytes. Third, a DXF is measured in a way an image never is: the coordinates are the real ones, so the recipient can measure directly on the drawing in their CAD program.
A DXF of a floor plan typically holds only three kinds of thing: lines (walls, frames, furniture outlines), arcs (a door's swing) and text (room names and areas). That sounds sparse, but it is everything a floor plan needs.
Layers are what make a DXF usable
The most important thing in a DXF is not the lines but the layers. A layer is a named group that the recipient can hide, lock, colour or select all of at once.
A usable floor plan in DXF has at least these layers kept separate:
- Exterior wall and interior wall — so you can see the shell of the house apart from what can be moved.
- Door, window and doorless opening — three different things that are priced differently.
- Room name and room area — text that a drawing office often needs to switch off once it lays its own lettering on top.
- Furniture — the first thing a recipient turns off when a new kitchen is being drawn.
If you receive a DXF where everything sits on layer 0, it is technically valid but far less useful: the recipient can't separate furniture from walls without clicking through the whole drawing. Ask for layered output when you order a DXF, and check it yourself before you send one on.
HouseSense writes DXF with walls, doors, windows, doorless openings, room names, areas and furniture each on their own layer, and lets you choose whether the layer names should be readable words in the recipient's language (WALL, VAEG, WAND) or code names under ISO 13567 with building-element numbers that a drawing office can map straight into its own template. Choose the codes, and the full key is written out in a cover sheet delivered alongside the file — nobody has to memorise them.
So why does DWG even exist?
DWG is the format AutoCAD saves in by default, and it predates DXF. It is binary, optimised for Autodesk's own program, and Autodesk has never published a free specification for it. Other programs read and write DWG either by licensing a library or by reverse engineering it — and the result is that DWG support is something you pay for, not something an app can simply do.
DXF came about precisely because DWG is closed: Autodesk itself needed a way in and out of AutoCAD that others could write against. That is why DXF is documented, and why an iPhone app can write a DXF but not a DWG. There is no usable way to write DWG on a phone without sending your drawings up to someone else's server to be converted — and an app that works entirely on your own device does not do that.
In practice the loss is small. Everything a floor plan consists of — lines, arcs, text, layers — is carried just as well by DXF. What DWG does better is the heavy machinery of a real project: xrefs to other drawings, dynamic blocks, layouts with multiple viewports. None of that exists in a survey of a home.
DXF versions: why the drawing office asks for R12 or 2013
DXF exists in editions named after the AutoCAD version they matched: R12, R13, R14, 2000, 2004, 2007, 2010, 2013, 2018. A newer program can read old DXF files, but an old program can't always read new ones.
R12 (AC1009) is the most widely read edition. It is simple, it can only hold lines, arcs, circles and text, and almost every piece of CAD software on the planet opens it. The price is that you can't save modern refinements in it — but a floor plan doesn't need them. That is why HouseSense writes DXF as R12: the file needs to open for whoever receives it, not only for whoever has the newest licence.
If you get a DXF you can't open, ask about the version first. The next thing to ask about is the unit.
Units: the mistake that makes the house 4 cm wide
A DXF stores numbers, and the unit only appears in the file if whoever wrote it set one. HouseSense writes the unit into the file (metres), but many other sources don't. Written in metres, a 4.12 m wall is stored as 4.12. Written in millimetres, it is stored as 4120. If the recipient opens a metre drawing in a program expecting millimetres, the house becomes 4 cm wide — and the other way round, it becomes 4 kilometres.
The fix is a single line in the email: "DXF in metres, R12, 2D plan, measured internally." Then the recipient handles the scaling in one second. Many drawing offices work in millimetres, so a metre drawing needs to be multiplied by 1000 on their end — that's a single scaling click, not a problem, as long as it's stated in the email.
Worked example: the living room measures 4.12 × 3.05 m. In a metre DXF the walls are stored as 4.12 and 3.05. The recipient scales by 1000 and gets 4120 × 3050 mm. The area stays the same: 12.57 m². Scaling only changes the unit of the numbers, never the ratio between them.
What DXF is not
Three misunderstandings are worth clearing up before you pass a DXF on:
- A DXF of a floor plan is 2D, not 3D. It is a horizontal cut through the house seen from above. If the recipient needs the room in three dimensions, that's a model file — OBJ, GLB, USDZ — not a DXF.
- A DXF is not a BIM model. In a BIM model (IFC, Revit), a wall knows it is a wall, what it's made of, and how thick it is. In a DXF, a wall is two lines 11 cm apart, and the layer name is the only thing saying what they represent.
- A DXF does not tell you whether a wall is load-bearing. If there's a layer named something like "load-bearing", that's a claim made by whoever drew it — typically the homeowner. Whether a wall actually carries load is decided by a building surveyor or a structural engineer, never by a drawing or an app.
When should you use DXF, and when should you use PDF?
In short: DXF for whoever is going to keep drawing on it. PDF for whoever just needs to read it. The architect, the drawing office, the kitchen company and the structural engineer need DXF. The carpenter, the painter, the flooring contractor and the bricklayer putting together a quote need PDF — it prints to scale and needs no software.
If in doubt, send both in the same email. A PDF of a floor plan is typically under 1 MB, and a DXF a few hundred kilobytes. It's cheaper to send two files than to wait two days for an answer about which one was needed.