Automatic
Pixel Ruler

Automatic Pixel Ruler captures your screen continuously, looks for flat areas, shapes and edges, and outlines every rectangle it finds: title bars, buttons, panels, images, table cells, sections of a web page, rooms on a floor plan. Move the mouse over one of them and its dimensions appear. Nothing to drag, nothing to click.

Most screen rulers measure one spot, under the cursor, when you ask. Automatic Pixel Ruler measures everything on screen at once, and keeps doing it while you work. Because it reads pixels, not the structure of an application, it works on anything Windows can display:

• Desktop applications and web pages.
• Remote desktops, Windows Sandbox, Hyper-V and other virtual machines, where no inspector can reach the application.
• Screenshots, mockups delivered as images, photos and paused video.
• Floor plans, drawings, maps and scanned documents, measured in real-world units.

Key Capabilities

Free and Pro

Automatic Pixel Ruler is free. Detection, highlighting, units, the special effects, presets and saving the highlighted elements are free and stay free. The optional Automatic Pixel Ruler Pro add-on, a one-time purchase in the Microsoft Store, adds the tools for measuring and reporting:

The title bar says Automatic Pixel Ruler Pro when the add-on is active, and the About dialog shows the edition. Using a Pro feature without the add-on shows a short notification next to the mouse pointer, and nothing else changes. Get the add-on with the Get Pro button of the About dialog.

System Requirements

When Automatic Pixel Ruler starts, its main window opens in the bottom-right corner of the primary monitor, and a transparent overlay covers the screen and starts detecting rectangles right away.

1. Start Automatic Pixel Ruler. Colored outlines appear around the rectangles found on screen.
2. Move the mouse over an element. Every rectangle under the pointer is highlighted with its width and height, for example 320 × 48.
3. Press Left Ctrl to step through nested rectangles under the pointer, a button inside a panel inside a window.
4. Press Right Ctrl to save the highlighted elements as PNG images.
5. Press Ctrl+Shift+X to draw a line and measure between two points, and Esc to stop.

Every action is confirmed by a short notification next to the mouse pointer. It can be turned off in Settings. The Keyboard Shortcuts button of the About dialog lists every key, see Keyboard Reference.

The status bar at the bottom of the main window shows how many rectangles were detected in the last frame, and how long it took. If the screen looks too busy or too empty, see Tuning Detection.

Outlines and highlights

Every detected rectangle gets a thin colored outline. The color comes from the rectangle's position, so a given element keeps the same color from one frame to the next.

Rectangles under the mouse pointer are highlighted: a thicker outline and a larger label with their width and height. When several rectangles are stacked under the pointer, the label also says which one it is, 640 × 480 (2/5) is the second of five highlighted rectangles.

One of the highlighted rectangles is the active one. It is drawn with a semi-transparent fill. Press Left Ctrl to make the next one active. Moving the mouse starts the list over.

Showing every dimension

By default only highlighted rectangles show a label, so the screen stays readable. The  button in the title bar of the main window puts a label on every detected rectangle, and  goes back to highlighted ones only.

Units and physical sizes

Dimensions are in pixels by default. In Settings you can switch to inches, centimeters or millimeters. Physical units are computed from the monitor's raw DPI, read from its hardware description (EDID), so a 5 cm label means 5 cm on the glass, whatever the resolution or the Windows scaling. This is what makes the app useful on floor plans and drawings displayed at a known scale.

When all displays are captured, each rectangle uses the DPI of the display that shows most of it.

Calibration (Pro)

Monitor DPI gives the size of what is on the glass. Calibration gives the size of what the image shows: millimeters on a scan, meters on a plan, microns under a microscope, whatever the zoom.

1. Display an image with a known length on it, a scale bar, a ruler, a dimensioned wall.
2. Press Ctrl+Shift+X at one end of that length, and move the mouse to the other end.
3. Press Shift+Left Ctrl. A dialog asks for the real length, for example 50 or 2,5, and its unit: µm, mm, cm, m, km, in or ft.

From then on every dimension, every length and every area is shown in that unit, until you choose another unit or click Clear Calibration in Settings. A calibration applies to images displayed at the same zoom, so calibrate again after zooming the image.

Measuring with lines

For lengths that are not rectangles, or to check a detected value, draw a line:

1. Put the pointer on the start point and press Ctrl+Shift+X.
2. Move the mouse. A line follows it, labeled with its length and with the horizontal and vertical span it covers, for example 125 px (100 x 75 px).
3. Press Ctrl+Shift+X again or Esc to stop.

While a line is being drawn, the labels of the detected rectangles are hidden, so the line and its own label stay readable. The shortcut can be changed in Settings.

Paths, angles and areas (Pro)

While a line is being drawn, keys on the left side of the keyboard turn it into a measuring tool, so the right hand stays on the mouse. They act when pressed and released on their own, so nothing else changes in the application you are measuring.

Every point placed is marked with a dot, the start point with a larger one, so you see where a line begins even before moving the mouse. With three points or more, the label also gives the area and the perimeter the shape would have if it were closed, and a thin line shows the side closing it would add. Bring the pointer back on the start point and the label shows the closed shape.

Kept measurements are numbered, #1, #2, and each has its own color. Numbers always run from 1 without gaps: deleting a measurement renumbers the ones after it. They stay where they were drawn on the screen and follow any change of unit or calibration. To delete one, put the pointer on its line or its label and press Shift+Left Ctrl. With the pointer on none of them, the same keys delete them all.

Automatic Pixel Ruler can save detected elements as PNG images, cropped exactly to the rectangle. The images come from the original screen capture, so they contain no outline, no label, and no pre-processing effect.

Files go to the Windows Screenshots folder, usually Pictures\Screenshots. They are named like this:

That is the app name, the date, the number of seconds since midnight, and the position of the rectangle in that save, starting at 0. All files saved by one key press share the same time stamp.

Each image carries its details, shown by File Explorer in the file's properties: the program, the date, and when a unit other than pixels is chosen, the size of the element in that unit as its title.

Exporting measurements (Pro)

"On a kept measurement" means the pointer is on its label, or close to one of its lines. Each export also writes a .csv file next to the image, with the same name. It opens in Excel directly as columns, and the table copied to the clipboard pastes into a spreadsheet the same way:

The images drawn for an export show the measurements only, without the outlines of the detected rectangles. Their details in File Explorer hold the measurement as the title and the table as comments.

An application window

A floor plan, calibrated

A drawing, paths and angles

Exporting measurements

Figures on a background

A remote desktop

A photo, with and without pre-processing

The main window is a compact panel that can be moved anywhere and resized horizontally. It has a title bar with buttons, a property grid with every detection parameter, and a status bar. The window itself is excluded from screen capture, so it never ends up in detections, saved images or recordings.

Dragged close to an edge or a corner of any monitor, the window snaps to it, leaving a small margin set in Settings. Keep dragging to pull it away. When its height changes, for example when you switch detection mode, it grows away from the nearest screen corner, so a window parked in a corner stays there.

1

Title bar

2

Sampling

3

Detection

4

Input display

5

Pre-processing

6

Special effect

7

Status bar

1

Title bar. Drag it to move the window. Its buttons are described below.

2

Sampling. How often frames are analyzed, see Tuning Detection.

3

Detection. Minimum size and edge thresholds, see Detection parameters.

4

Input display. The monitor to measure, or all of them. Only shown when more than one display is connected.

5

Pre-processing. Image clean-up before detection, see Pre-processing.

6

Special effect. None, Pixel, Oil or Crystal, with their own parameters, see Special effects.

7

Status bar. Rectangles detected in the last frame and the time it took, and confirmation messages.

Title bar buttons

•  About, with system information, this guide and the Microsoft Store page. See Support & Licensing.
•  Settings: units, the manual measurement shortcut, and presets. See Settings & Presets.
•  Reset every detection parameter to its default value, after a confirmation.
•  /  Pause or resume capture. While paused, the overlay and its measurements are gone, which is handy to change settings or use the screen normally.
•  /  Label every rectangle, or only the highlighted ones.
•  /  Show the pre-processed image in the overlay, or the original screen. The pre-processed image is what the detector actually sees.

Editing values

Every parameter applies immediately. Drag a slider, or click the number next to it and type a value. While typing, Up and Down change the value by 1. Drag the column divider to resize the names and values columns.

The defaults work well on ordinary application windows. Photos, drawings and busy pages usually need a few adjustments.

Detection mode

The first setting of the main window chooses how rectangles are found. Each mode suits a different kind of content.

Areas and Objects work on the original screen, so the edge thresholds, the pre-processing and the effects only apply in Edges mode, and they are hidden in the other two. Presets remember their mode.

How Edges mode works

1. Capture. The selected display is captured by the GPU, frame after frame.
2. Pre-processing. A GPU shader simplifies the frame: posterization, color reduction, blur, sketch and an optional special effect.
3. Detection. Edges are found with a Canny detector, then grouped into outlines, and each outline gives a bounding rectangle. Rectangles that are too small, or that cover the whole screen, are dropped.
4. Rendering. The overlay draws the outlines and labels on top of the screen.

Advanced settings

A few settings are only useful for fine control, and they are hidden until Advanced Settings is checked in Settings: sampling, the weak edge threshold, blur quality and Oil sampling quality. While they are hidden, sampling stays adaptive and the weak edge threshold is half the edge threshold, so nothing invisible keeps acting.

Sampling

With Adaptive Sampling on, the default, the interval between two analyzed frames follows how long the previous ones took to process, which keeps the load in check. With it off, Fixed Sampling sets the interval between two analyzed frames, from 0 to 2000 ms, 1000 ms by default.

Detection parameters

Lower thresholds find fainter edges and more rectangles, higher thresholds keep only the sharpest ones. The pair works together: the weak threshold stitches broken outlines, the strong one decides where outlines start.

Pre-processing

Special effects

An optional effect applied before detection. Each one is meant for a different kind of picture.

Starting points

Building a preset for your kind of images

Every kind of image has its own look. Scans, floor plans, microscope images, maps, photos and user interfaces all differ in contrast, noise, texture and line thickness, and no single setting fits them all. The parameters above, and the special effects in particular, are how you teach Automatic Pixel Ruler what matters in your images and what to ignore. Getting it right takes a little practice, but you only do it once per kind of image.

1. Open a typical image of the kind you work with, one that has the shapes you want to measure.
2. Turn on the pre-processed view , so that you see what the detector sees while you adjust.
3. Simplify the image first. Lower the posterization and color levels, and add blur, until noise and texture fade while the outlines you care about remain.
4. Try each special effect. Oil tends to suit photographic and scanned content, Pixel hides text and fine detail, Crystal marks the borders of irregular shapes. Adjust the effect's own parameters until the outlines are clean.
5. Adjust the edge thresholds, then raise the minimum size until only the shapes you want are left.
6. Check the result on two or three other images of the same kind, and correct what they reveal.
7. Save the settings as an .apixruler preset with a name that says what it is for, for example scans.apixruler or floorplans.apixruler.

From then on, loading the preset brings back the whole configuration in one step. A preset is also the easiest way to share this work: once one person in a team has tuned it, everyone who opens the file gets the same detection. See Presets.

Click  in the title bar to open the Settings dialog.

• Dimensions unit. Pixels, inches, centimeters or millimeters, see Units and physical sizes. When a calibration is active, the calibrated unit is shown instead, with a Clear Calibration button.
• Draw line shortcut. The key combination for drawing lines. It must include Ctrl and must not be used by another application. An invalid combination is refused and the previous one is kept.
• Snap Margin. The gap left between the main window and the screen edge it snaps to, from 0 to 200.
• Show Notifications. The short messages next to the mouse pointer. When they are off, the status bar still shows them.
• Show Areas. Adds the area to the label of every rectangle, for example 12 x 8 cm, 96 cm².
• Save settings and Load settings, to write the detection parameters to a preset file, or read them back.
• Advanced Settings, to show the settings meant for fine control, see Advanced settings.

Presets

A preset is an .apixruler file holding every detection and pre-processing parameter. Keep one per kind of work, one for application windows, one for photos, one for plans, and load the one you need. Presets are plain JSON files and can be shared with colleagues or copied to another computer.

To open presets with a double-click, right-click an .apixruler file in File Explorer, choose Open with, then Choose another app, select Automatic Pixel Ruler and check Always.

Resetting

The  button in the title bar resets every detection parameter to its default value, and clears the calibration, which brings dimensions back to pixels. The other units, the shortcut and the selected display are kept.

These keys work anywhere while the app is running, even when another application has the focus. Left Ctrl, Right Ctrl and Left Shift act when they are pressed and released on their own, so shortcuts in other applications, such as Ctrl+C or a capital letter, never trigger them. Left Shift only does something while a line is being drawn.

The Keyboard Shortcuts button of the About dialog shows the same list in the application, with the key names of your own keyboard.

While a line is being drawn:

To start over from factory settings, close the app and delete settings.json. Captured frames never leave your computer. They stay in GPU memory and are only written to disk when you save an image.

Windows 10

On Windows 11 the overlay is invisible to the mouse and the keyboard, and you can keep working in your applications while measuring. Windows 10 does not allow that for this kind of overlay, so while capture is running the overlay takes the mouse and keyboard input.

The taskbar and Alt+Tab still work. To use an application, click  to pause capture, then  to resume measuring.

Click  in the title bar to open the About dialog.

Under the version, the dialog says whether this is the free edition or the Pro edition.

• System Info lists your displays, their DPI, and the app's configuration. Copy it into a support request.
• User Guide opens this page.
• Keyboard Shortcuts lists every key, and where images and exports are saved.
• Get Pro, in the free edition, lists what Pro adds and opens the Microsoft Store purchase of the add-on. In the Pro edition, Go to Microsoft Store opens the app's Store page instead, to leave a review or get support.

Pro is a one-time purchase tied to your Microsoft account, like the app itself. It is recognized on every Windows computer where you sign in to the Microsoft Store with that account.

If the app runs into an unexpected error, it offers to write an anonymous error report to your desktop. Nothing is sent automatically, you decide whether to send the file.