Measure on screen in centimeters, millimeters, inches and pixels. Calibrate against a physical reference, cross-check the display scale, measure spans, and use fullscreen.
Actual-size calibrationphysical-reference matching rather than trusting 96 CSS px/in
CM · MM · IN · PXmeasure the same span in physical and screen units
Independent PPI cross-checkcompare saved calibration with a diagonal/spec estimate
Confidence boundarysee placement resolution and environment mismatch before trusting a reading
Calibrated physical-size workflow
Ruler Calibration & Measurement Studio
Match a known real object on this display, verify the current environment, then measure spans in CSS pixels and physical units. Physical-size readings are intentionally marked approximate until this display is verified.
ID-1 card referencemm · cm · in · 1/16″ · pxEnvironment guardLocal history + JSON/CSV
1. Calibrate this display
85.60 mm reference
Scale—
Effective density—
VerificationNot verified
Last verifiedNever
Current environment—
Physical size is approximate until the selected reference is matched and verified on this display.
2. Cross-check display geometry
This optional check compares the calibrated CSS scale with a diagonal/native-resolution estimate. OS scaling, display modes and browser zoom can make the two disagree, so this is evidence—not a certification.
Diagonal estimate—
AgreementNeed inputs
Difference—
3. Measure on the ruler
Drag on the ruler to set a two-point span. With the ruler focused, arrow keys nudge the end point by 1 CSS pixel; Shift + arrow nudges by 10. This makes small adjustments reproducible without pretending CSS pixels are physical pixels.
Millimeters—
Centimeters—
Inches—
Nearest 1/16″—
CSS pixels—
Drag on the ruler to measure.
4. Measurement history
Keep up to 20 measurements in this browser. Each row records whether the physical scale was verified at measurement time.
Time
CSS pixels
Physical length
Orientation
Action
No saved measurements.
5. Save, import or share the setup
Calibration JSON and Workbench JSON are portable data, but verification never transfers. A receiving display must physically match a reference again.
Accuracy boundary: browser CSS pixels are not guaranteed to equal physical pixels. Page zoom can change devicePixelRatio behavior, pinch zoom has its own visual viewport scale, and OS/display scaling can change apparent size. Re-check calibration after moving the browser to another display, changing zoom/scaling, using remote desktop, or after 30 days. For engineering, medical, machining, safety-critical or legal measurement, use a calibrated physical instrument.
CSS pixels are a layout unit, not a promise of physical size. Match a known physical reference on the exact display you will use, then treat millimeter and inch output as valid only while that environment remains verified.
ID-1 reference dimensions
The Studio offers the common ID-1 card nominal edges, 85.60 mm and 53.98 mm, as convenient reference choices. Real cards can be worn or manufactured within tolerances, so precision work should use a traceable physical standard.
What the display cross-check can and cannot prove
A diagonal/native-resolution PPI calculation is useful corroborating evidence, but OS scaling, display modes, browser zoom and remote sessions can change the relationship between reported pixels and physical size. That is why imported or shared calibration is always downgraded to unverified.
WebToolArc