How to scale a converted DXF drawing using a known dimension
Calibrate image-to-DXF pixel units and PDF paper millimetres. A worked scale-factor example and checks for scanned engineering drawings.
Why is my converted DXF the wrong size?
Image-to-DXF coordinates use source image pixels. PDF-to-DXF coordinates represent millimetres on the PDF paper. Neither automatically establishes the real part size. A drawing printed at 1:5 or resized during scanning needs calibration before engineering use.
Calculate the scale factor
Choose a clear, trustworthy dimension on the original. Measure the same two endpoints in the DXF. Divide the intended real length by the measured length. For example, if a known 50 mm edge measures 250 drawing units, the uniform scale factor is 50 / 250 = 0.2. This is a calculation example, not a measured accuracy claim for the converter.
Apply and verify the scale
Set the intended units in your CAD application, select the relevant drawing entities and apply uniform scaling around a suitable reference point. Then measure an independent known dimension, preferably in the other direction. If the first dimension matches and the second does not, inspect endpoint selection, source distortion and drawing proportions.
When uniform scaling is not enough
Photographs taken at an angle can have perspective distortion. Stretched scans may have different horizontal and vertical scales. Do not force a single dimension to fit and assume the rest is accurate. Use a flatter, higher-quality scan or request a refinement assessment with explicit dimensional checks.
What should be checked before reuse?
Check units, at least two independent dimensions, holes, arcs, missing or duplicate boundaries and recognized text. DXF export does not automatically reconstruct design constraints, tolerances or manufacturing intent. Start with a PNG, JPG or selected PDF page up to 1 MB, then review the actual conversion result in your CAD software.
The free tool accepts PNG, JPG/JPEG and PDF files up to 1 MB, processing one selected PDF page per conversion. Guests get 1 conversion per IP per day; signed-in accounts get 3. Allowances reset at 00:00 China Standard Time (UTC+8); failed jobs return the allowance. Network abuse-prevention limits also apply.
Online source files, results and previews are deleted 30 minutes after task creation. Private review copies are deleted after 48 hours. Download and keep your own copy in time.