PCB Gerber Wrong Size? Check Units and Board Outline

If a Gerber preview reports a board much larger or smaller than your design, do not compensate by typing a different size into the quotation form. First establish whether the error is in the exported geometry, the viewer interpretation or the distinction between one board and a panel. The manufactured outline and your order dimensions must agree.

Start with one known measurement

Choose a distance that is easy to identify, such as the separation between two mounting-hole centers. Compare that distance in the PCB editor, a separate fabrication viewer and the dimensioned mechanical drawing. A screenshot scaled to fit a browser window is not a measurement. Use the viewer's measurement function and record its unit.

An exact factor of 25.4 is a useful clue for an inch-to-millimeter mismatch. It is a diagnostic clue, not permission to rescale every file. Copper and drill files can have different interpretation problems, so check both before changing export settings.

Look for geometry outside the intended board

Display the outline alone. Look for a copied board far from the origin, a dimension line exported on the contour layer, an open segment or an extra rectangular frame. Then overlay the copper and drill files. A correct contour with displaced drills suggests an origin or export problem rather than a wrong board dimension.

• Confirm there is one intended outer contour for a single board.
• Identify every internal cutout separately from the outer boundary.
• Remove explanatory drawings from the fabrication contour output.
• Check that the file being previewed belongs to the current revision.

Distinguish a board from a delivery panel

For example, a 40 × 30 mm board repeated in an array should not be ordered by entering 40 × 30 mm while uploading a complete panel without explanation. Provide both the individual-board dimensions and the panel drawing. State the number of boards per panel and whether your requested quantity counts boards or panels.

Re-export and close the discrepancy

Correct the source design or export configuration, generate a complete new release into an empty folder, and reopen the new archive. Avoid replacing only the contour while leaving old drills behind. If two viewers still disagree, send the archive, the expected dimensions and annotated screenshots to the file-review team. Ask which geometry they will manufacture before approving production.