Comparing two revisions of the same drawing
The two panes above are independent viewers sharing one camera. Load the older revision on the left and the newer one on the right, and every pan, zoom and orbit in one pane is applied to the other, so both drawings stay framed identically as you work across the sheet. Both files are read from your disk by the browser and parsed locally — nothing is uploaded, there is no account, and there is no limit on how many pairs you check.
Why comparing CAD drawings matters
Drawings change constantly, and the record of what changed is rarely as complete as the process assumes. Comparing two issues of the same sheet turns an assumption into a fact.
Revision control
A sheet reissued as Rev C should carry clouds and a note describing what moved. In practice the note reads general revisions and the clouds cover half the plan. Rev B beside Rev C gives you the specifics.
Checking what a subcontractor changed
You issue a drawing for coordination and it comes back marked as updated. Whether a duct was rerouted or a leader line nudged decides whether you re-run a clash check or sign it off.
Verifying an as-built against the design
As-built drawings are meant to record what was installed. Comparing them against the design issue exposes where site deviated — a wall set out 200 mm off, a diverted drainage run, an omitted riser.
Catching an unannounced revision
A file appears in the project folder with the same name and a newer date, and no transmittal explains it. Check it against the copy you have been working to; silent revisions are the expensive ones.
The same check is worth running after a format round trip. A DWG exported to DXF for a laser cutter can lose entity types quietly, and loading the original beside the export shows what survived — our DWG vs DXF comparison explains why.
How to use the comparison tool
- Load File A. Click Upload File A in the left header, or drag a DWG or DXF onto the left pane. The drawing is fitted to the pane automatically.
- Load File B. Do the same on the right. Once both panes hold a drawing, the right pane adopts the left pane's camera, so the two views start aligned.
- Navigate once, see both. Left-drag orbits, right-drag pans, the scroll wheel zooms; whichever pane you act on, the other follows immediately.
- Isolate a discipline. Each pane has its own Layers button top-right, and unchecking a layer hides it in that pane only. Leaving just the electrical layer visible in both panes strips out grids, hatching and title block noise.
- Sweep the sheet. Zoom into a region, read across both panes, then move on. Your eye moves between two identical frames instead of holding a whole drawing in memory.
Alignment depends on both files sharing a coordinate origin, which two revisions of the same drawing normally do. If someone rebased the drawing or moved it to a new insertion point, the panes will show identical coordinates but visibly different content. That is not a fault in the tool — it is a finding, and usually an important one.
What this comparison is, and what it is not
This is a synchronized visual comparison, not an automatic geometric diff. It does not calculate which entities were added, deleted or moved, it does not highlight changed geometry in colour, and it produces no change list or overlay. Your eyes do the comparing; the tool holds both drawings in the same view so they get a fair chance. There is no hidden mode that does more.
Other limits are worth knowing before you rely on a check made here. These panes read DWG and DXF only; measurement, markup, text search and export live in the main viewer. Xrefs are not resolved, so anything inside one is absent from both sides. Proxy objects from Civil 3D or Advance Steel do not render, custom SHX fonts are substituted, complex hatches show as boundary outlines, and DIMENSION entities in DWG files may not draw at all. Those limits apply to both panes equally, so a missing entity type will not masquerade as a change — but do not conclude that a dimension was deleted when neither pane draws dimensions at all.
A practical workflow for checking a revision
Comparing by eye works well when it is systematic and badly when it is not. This sequence takes a few minutes on a typical sheet.
- Fix the order. Older revision left, newer right, every time — then a difference immediately tells you whether something was added or removed.
- Full extents first. Sheet outline, footprint, north arrow, grid extent, density of linework. Large omissions are only visible from a distance.
- Read the title block. Revision letter, issue date, scale, drawn-by, revision note. A scale or paper size change explains differences you would otherwise chase for twenty minutes.
- Compare the layer lists. A layer present on one side and absent on the other is the fastest signal that content was added or deleted wholesale.
- Go discipline by discipline. Hide everything but one layer in both panes and sweep: structural grid, walls, services, annotation.
- Sweep in grid bays. A reversed door swing, a re-anchored dimension string or a thickened wall is invisible at full extents and obvious at bay scale.
- Record findings as you go. These panes have no markup layer. For an annotated image, open the file in the main viewer, add arrows and text, and export a PNG or PDF.
A visual comparison is a fast, honest check, not a certified one. If a difference will support a variation claim, verify it in a full CAD package with a drawing-compare command. Use this page for the everyday question — what changed, and does it affect me.
Load two files and try it now
The sample drawings are free to download and open in any CAD package as well as here. Download two, then drag one into each pane above to learn the controls before using the tool on live work.
The samples are separate drawings rather than two revisions of one drawing, so they will not overlay. For a realistic rehearsal, export the same drawing from your own CAD twice with one small edit in between, then compare those two files here.
Frequently Asked Questions
Can I compare two DWG or DXF files online for free?
Yes. Load one drawing into each pane and navigate them together. There is no signup, no paid tier, no watermark and no cap on how many comparisons you run. Both files are read from your disk by the browser and parsed on your own machine. The panes accept DWG saved by AutoCAD R14 through 2026 and ASCII DXF.
Does this highlight the differences automatically, like a DWG diff?
No, and it is worth being blunt about it. This is a synchronized side-by-side view, not an automatic geometric diff. It does not compare entity lists, work out what was added or deleted, or colour changed geometry red and green. It gives you two drawings locked to the same camera with independent layer control, so a human can find differences quickly. A computed change report needs a full desktop CAD package with a drawing-compare command.
Why do my two drawings not line up in the panes?
The panes share a camera, so they always show the same world coordinates, and two files line up only if their geometry sits at the same coordinates. Each drawing is fitted to its pane on load, then the right pane adopts the left pane's view, so revisions of the same sheet normally align by themselves. If they do not, the drawing was rebased, moved to a different insertion point, or drawn in different units — a genuine difference between the files rather than a display problem.
Can I compare a DWG against a DXF of the same drawing?
Yes. Each pane detects the format from the file extension, so a DWG on one side and a DXF on the other is fine. This is a useful check after an export, because it shows what survived the conversion before you send the DXF to a fabricator. Bear in mind that some differences come from the formats rather than from the drawing: proxy objects, custom fonts and complex hatch patterns do not always cross over cleanly.
Are my drawings uploaded to a server when I compare them?
No. Both files are read in the browser with the FileReader interface and parsed by JavaScript and WebAssembly on your own machine. Nothing is transmitted and no copy of either drawing exists anywhere but your device. That matters for revision checking in particular, because the drawings involved are often confidential and the comparison usually happens before anything has been formally issued.
Can I export or print the side-by-side comparison?
Not from this page. The comparison panes carry layer control but no export. If you need an image for an RFI or an email, open the file in the main viewer, mark it up with arrows, rectangles or text, and export a PNG or a PDF from there. Both exports are raster snapshots of the viewport and the PDF is A4 landscape, so treat them as a record of what you saw rather than a plotted drawing.
Related pages
Need the full viewer instead?
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