Measure module

The Measure tool lets you quantify distances directly on a PDF page, in the manner of a virtual ruler. It is designed for common technical uses: checking the size of a graphic element, verifying a dimension on a drawing, measuring a margin before printing, and so on. You reach this module from the Editing category of the Dashboard.

How to use it

Open the Measure module from the Dashboard;
Choose the display unit in the sidebar (see below);
In the PDF view on the left, click and drag between two points to draw a segment;
The length of the segment is shown on screen in the chosen unit.

The tool stays active as long as the module is open: you can chain several successive measurements without running a command each time — but only one is shown at a time, each new drag clears the previous one. Leaving the module automatically disables measurement mode and restores the classic text-selection behaviour.

Choosing the unit

A segmented selector offers three units of measurement:

pt (points) — the native unit of the PDF format. 1 point = 1/72 inch ≈ 0.353 mm. Handy for precise dimensions on technical PDFs where elements are sized to the point;
in (inches) — the anglophone unit (″). 1 inch = 72 points = 2.54 cm;
cm (centimetres) — the metric unit. 1 cm ≈ 28.35 points.

The chosen unit applies to the next measurement: a segment already on screen keeps the unit it was drawn in; draw it again to read it in the new one.

Accuracy and calibration

Measurements are computed from the geometric size of the PDF document, as recorded in the file (the MediaBox). That means that:

for a digitally generated PDF (a Word or InDesign export, an AutoCAD drawing), the measurements match the physical dimensions when printed;
for a PDF produced by a scan, the measurements depend on the resolution and framing of the scan. An A4 page scanned at 300 dpi will keep its 21 × 29.7 cm, but an imperfect scan (a page not lying flat, approximate framing) can introduce slight inaccuracies.

The tool exposes no explicit calibration mechanism against a reference: it always trusts the PDF document's coordinates. For fine technical measurements on a scanned document, first check that the dimensions shown on the Dashboard (information area) are consistent before taking any decision based on a measurement.

Typical use cases

Architectural drawings: quickly checking a dimension on a drawing exported to PDF (remembering to use the appropriate metric unit and to take the original drawing's scale into account);
Layout: measuring the effective margin of a document before printing, or the size of an inserted image;
Official documents: checking that the signature area respects an imposed dimension (administrative forms, and so on);
Technical PDFs (CAD, schematics): validating a distance between two elements without reopening the source file.

Known limitations

The tool measures straight-line distances only. It does not (at this stage) offer perimeter, area or polyline path measurement;
Measurements are not saved as annotations in the PDF: they are shown as an overlay in the view but disappear when you change page or close the module. To keep a written record of a dimension, then create a Note annotation in which you record the measured value, or a text Stamp stating the dimension;
Measurements do not take into account any scale of an architectural drawing. A dimension drawn on a 1:100 plan will measure the printed dimension of the drawing, not the real dimension represented. Do the scale calculation manually if needed.

Note: for demanding metrological surveys or measuring areas and perimeters, specialised PDF tools (e.g. Bluebeam Revu, PDF Annotator) remain preferable. HtkPDF's Measure module is sized for quick everyday checks.

Screenshots

1 screenshot — click to enlarge