Accurate page scales are essential for precise measurements. If a PDF page or multiple pages in a document include embedded scale information, you can measure objects using the embedded scale on each page. Before doing so, enable the Use Scale and Units From Document (When present) option in File > Preferences > Measuring.
With this option enabled, when a page does not contain an embedded scale, the Apply Scale to More Pages dialog box appears when you place your first measurement, prompting you to set or calibrate a scale manually.
In the Apply Scale to More Pages dialog box:
- Choose the page range to apply the scale to.
- Specify a scale using either of the following:
- Preset: Select a predefined scale.
- Custom: Create a custom scale by entering the drawing length and unit on the left side of the scale equation, and the real-world length and unit on the right. To save the scale as a preset for future use, select Add Preset.
- (Optional) If you are unsure whether the PDF was scaled correctly, calibrate the scale:
- Click the Calibrate button next to the scale.
- Locate a known dimension on the page. Click the first point, then the second point to draw a line. Tip: When drawing, you can hold down SHIFT to snap the two points horizontally, vertically, or diagonally. You can also choose a snapping type from the Measure sub-tab in the Format tab to capture the path on the page.
- The Calibrate dialog box pops up. The measured length is shown on the left side of the scale equation. Enter the real-world distance for those two points and select the units on the right.
- If needed, click Recalibrate to perform the calibration again.
- (Optional) To set separate X and Y scales, select Separate Y Scale, and then set the Y scale. Note: If you later deselect Separate Y Scale, the X scale applies to both axes for future measurements. Existing measurements are not affected.
- Select the measurement precision from the Precision drop-down list. Precision is expressed as a decimal or fraction depending on the scale (or the X scale when separate scales are used).
Click Apply Scale.
The new page scale will be embedded into the page or pages selected, replacing any existing embedded page scale. Measurements update accordingly.
With the Use Scale and Units From Document (When present) option unselected, you can define a custom scale ratio in the Measure sub-tab in the Format tab. The defined scale ratio will only be applied to the current page.
Tip: Always confirm the scale before measuring. If the PDF contains multiple drawings at different scales, set the correct scale for each page.