Gerber Viewer & Compare

Inspect one PCB layout or compare two revisions. Open Gerber files or ZIP archives, select layers independently, and highlight geometry present only in A or B. Files stay on your device.

Method, formulas and references

Inspect one layout or compare two revisions

Open individual Extended Gerber layers, several selected files, or a ZIP containing layers. Layout B is optional. Each layout has its own visibility checkboxes and layer colours under Properties. The initial selection favours top copper; filenames, legacy image names and available X2 FileFunction attributes help identify layers, but you choose which layers to compare.

How the colours are calculated

Layers view draws the selected files in their individual colours. With at least one selected layer in both A and B, Overlay shows common geometry in grey, A-only geometry in orange and B-only geometry in blue. Differences only hides the common geometry. Each side is the union of its selected layer images: an overlap between different selected layers can hide a change, so compare matching layers when reviewing revisions. This compares rendered geometry, not file text, netlists or electrical intent.

Fullscreen and movement

Fullscreen expands the board view together with its layer and alignment controls. Escape or Exit fullscreen returns to the normal workspace and keeps your selections. On narrow screens the controls sit below the board. Dragging and wheel or pinch zoom use a lightweight preview; the original artwork is redrawn after movement stops. PNG export becomes available when that detailed frame is ready.

Coordinates and resolution

Gerber units are normalised to millimetres and original coordinate origins are preserved. No independent centring, automatic rotation or bottom-layer mirroring is applied. Positive B X moves right; positive B Y moves up. Fit only changes the camera. The selected geometries are rasterised on one shared viewport pixel grid, then compared at a 50 % coverage threshold. Anti-aliasing and the displayed pixel size limit the smallest visible change; zoom in and inspect the original layers before drawing conclusions.

Copper distribution

Copper analysis measures each chosen copper layer within a closed board profile. Profile strokes are interpreted as contour centre lines; enclosed cutouts are excluded using even-odd nesting. Open, branching, overlapping or crossing contours are rejected. Choose a dedicated contour or region profile without dimensions, aperture flashes, repeats or polarity masks. Circular arcs are flattened with at most 2 µm chord error.

Coverage is the projected copper area inside the profile divided by board area, multiplied by 100. Original composited copper artwork is sampled on a fixed physical grid, including clearances and overlaps. Alpha-weighted boundary samples estimate area; Standard requests 50 µm pixels and Fine requests 25 µm. Large boards use a coarser grid to stay within 8 million pixels and 8192 pixels per side; the actual resolution is shown. Small features below that resolution may be missed. Colours, visible layers, viewport zoom and layout B alignment do not affect these measurements. Drill files are not automatically subtracted. Compare corresponding layers explicitly; a coverage difference is reported in percentage points and each revision uses its own profile area.

Supported input and import notes

The viewer uses the MIT-licensed tracespace gerber-to-svg renderer for Extended Gerber paths, flashes, standard apertures, aperture macros, regions, clear/dark polarity and step-and-repeat. X2 attributes and legacy image names are used as labels where present. Older image-name and layer-name comments, default image transforms and positive-polarity declarations are accepted. Combined format/unit headers are normalised. Gerber job manifests contain metadata and are skipped when selecting artwork. Aperture blocks, non-default image transforms and negative-image files remain unsupported. Drill input supports decimal coordinates, FILE_FORMAT comments, KiCad FORMAT comments and unit-line zero patterns; units and precision are not guessed. Unsupported or invalid layers are reported in Import notes, while successfully read layers remain available.

Gerber and drill artwork are separate layers here: drill holes are not automatically subtracted from copper. Mask layers show the exported mask artwork, not a reconstructed finished board. A displayed image is not a fabrication approval or an exhaustive format-conformance check.

Files stay on your device

Files are read and parsed locally in a cancellable worker. Selected data remain in this tab's memory when switching tools, and are cleared by reloading or Clear. No board data or filenames are uploaded, stored in browser storage, or included in shared URLs. The PNG button exports the current view with selected filenames, colours, alignment and pixel resolution.

References

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Electronics

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Utilities

Gerber Viewer & Compare – Inspect one Gerber layout or compare two PCB revisions, choose layers independently and highlight added, removed and common geometry. Files stay on your device.
Unit Converter – Length, copper weight, temperature, power (dBm/W/V) and frequency/wavelength.
Reference Charts – Drill sizes (number, letter, fractional, metric), ISO metric and Unified threads with tap and clearance drills, and the AWG wire table.