1Local Privacy · Ctrl+V Paste
Upload a Photo or Paste a Screenshot
Click Open Photo Mode or press Ctrl+V anywhere in the workspace to load PNG, JPEG, or WebP images straight from memory without uploading files to a remote server.
Image Metrology · 100% Client-Side · Ctrl+V Clipboard Support
Measure Any Photo or Clipboard Screenshot Online
Drop an image or press Ctrl+V, mark any known reference length (credit card, coin, or A4 sheet), and measure spans, bounding boxes, and angles privately in your browser.
Interactive Online Screen Ruler Workspace
Embed Ad-Free Online Ruler (<iframe>)
cm
Origin (0, 0) · Top-Left Dashed Datum
Align your object with the 0 tick mark. Click any ruler or grid to drop draggable measurement guides.
100% Client-Side Photo & Clipboard Ruler
Press Ctrl+V to paste a screenshot, drop an image here, or choose a file. Nothing is ever uploaded.
Live Unit Converter@ 96.0 PPI
3 3/8 in (3 3/8 in)
Display Density Calibration · Saved Locally Per Screen
Calibrate Your Screen for True Physical Scale
Browsers default to 96 CSS pixels per inch, which rarely matches physical display panels. Choose one of the three calibration methods below so every millimeter and fractional inch tick corresponds to actual physical length.
Active ScaleEstimated calibration
96.0 PPI·3.780 px/mm
CSS reference scale (96 px per inch)
Display Profiles:
ISO/IEC 7810 ID-1 Standard · 85.60 × 53.98 mm
Align a Physical Bank, Credit, or ID Card
Hold any standard payment card, driver’s license, or national ID card flat against the outline below and match its physical width.
Target:
Drag the blue corner handle or slider to match your object
Top-left card alignment datum · 1:1 physical outline
ISO/IEC 7810 ID-1
85.60 mmPlace Physical Card Here
Align left & top edges · Match outer border
3.370 × 2.125 in53.98 mm
Optical Alignment Checklist
- Hold card flat: Place a real credit or ID card flush against the top-left corner of the box.
- Match outer edge: Drag the slider or press ← → keys until the right edge aligns exactly.
- Avoid parallax: Keep your eyes perpendicular to the right edge of the card.
Computed Scale: 96.0 CSS PPI · 3.780 px/mm
Keyboard fine-tuning: click the card stage and press ← → (Shift for 5px steps).
Geometric Display Calculation · √(W² + H²) / Diagonal
Calibrate by Visible Display Diagonal
Enter the diagonal measurement of your visible screen panel in inches (corner to corner inside the bezel, not the outer laptop chassis). Ensure browser page zoom is at 100%.
Common Display Diagonals (Inches)
Accuracy notes for diagonal calibration:
- Display vs. Device Body: Enter the active panel diagonal (e.g., 13.6″ or 15.6″), not the external case dimensions.
- Logical CSS Pixels vs. Physical Pixels: Operating systems often scale HiDPI panels (such as 125% or 150% on Windows, or “Looks like” Retina scaling on macOS). The browser reports logical CSS pixels at 100% browser zoom, which this calculation uses directly.
Browser Display Telemetry & Hardware Database
Automatic Device & Screen Density Detection
Online Ruler Plus inspects your browser’s reported logical screen dimensions, device pixel ratio, orientation, and platform to match known hardware profiles or compute a sensible initial estimate.
- Detected Profile
- Checking display…
- Detection Status
- Estimated calibration
- Estimated Density
- 96.0 CSS px/in
- Screen CSS Size
- —
- Device Pixel Ratio
- —
- Orientation
- —
Why verify manually? Web browsers do not expose physical monitor sizes over HDMI/DisplayPort or custom OS scaling factors. Always verify with a physical card or known diagonal before critical measurements.
Physical Verification Gauge
Verify With Everyday Objects
Hold a real coin against these live-scaled reference outlines to confirm your calibration immediately.
24.26 mm
US Quarter23.25 mm
€1 Euro19.05 mm
US Penny50.0 mm Reference Bar (5.0 cm)1.969 in
Local Session Log
Measurement History
Place two parallel guide lines in the ruler workspace and click Save to History to record point-to-point spans (ΔX / ΔY) locally on your device.
Storage: localStorage onlyZero network sync
Private Browser Image Metrology · Zero Server Upload
How to Measure Lengths & Bounding Boxes Inside Photos
Turn floor plans, hardware photos, microscopy snaps, and UI screenshots into scaled measurements locally on your device.
22-Point Image Scale
Set Reference Scale Inside the Picture
Pick two points spanning a known object in the photo (for example 85.60 mm across a bank card or 25.0 mm along a ruler tick) and enter its real length to lock in photo px/mm.
3Guides, ΔX/ΔY & Export
Measure Spans & Export Annotated PNG
Drop parallel guides, inspect bounding-box width × height in cm/mm/in/px, adjust image opacity, and save an annotated PNG with embedded measurements.
Measuring Objects Using Photo Measurement
FIG. 05 · PHOTO MODE
Two-Point Reference Calibration on Local Photos
LIVE UI · PHOTO MODE
Photo Calibration References · Common Benchmarks
Accurate Known-Size Objects to Include in Photos
Including one rigid flat reference next to your subject compensates for camera distance and lens zoom in any smartphone photo.
Avoid perspective tilt
Hold the smartphone camera directly perpendicular above both the reference card and the target object on the same flat table plane.
Pinch-zoom & Ctrl+V speed
Screenshots pasted with Ctrl+V retain exact pixel dimensions, making UI mockups, CAD exports, and PDF clippings effortless to measure.
Zero cloud storage
Images are decoded via URL.createObjectURL inside browser RAM and discarded automatically when you clear or close the tab.
Quick Photo Reference Lengths
Standard Everyday Reference Objects for Two-Point Calibration
| Reference Object | Exact Length (mm) | Inches (in) | Best Use Case |
|---|---|---|---|
| ISO ID-1 Bank / Credit Card Width | 85.60 mm | 3.370 in | Tabletop parts & crafts |
| ISO ID-1 Bank / Credit Card Height | 53.98 mm | 2.125 in | Compact vertical spacing |
| US Quarter Coin Diameter | 24.26 mm | 0.955 in | Coins, rings & small PCB boards |
| US Penny Coin Diameter | 19.05 mm | 0.750 in | Macro close-up fasteners |
| 1 Euro Coin Diameter | 23.25 mm | 0.915 in | European macro tabletop parts |
| AA Battery Length (IEC R6) | 50.50 mm | 1.988 in | Workshop & tool photos |
| US Letter Sheet Short Edge | 215.90 mm | 8.500 in | Furniture & floor mats |
| ISO A4 Sheet Short Edge | 210.00 mm | 8.268 in | Architectural sketches & parcels |
Place reference object flat beside target at equal camera distance to keep foreshortening below 1%.
Switch Ruler Axis or Unit Scale
Explore Other Calibrated Online Ruler Modes
Metric · cm
Centimeter Ruler
1 cm & 0.5 cm scale + cm-to-inch chart
Imperial · 1/16″
Inch Ruler (12″)
1/2, 1/4, 1/8, 1/16″ fractions
Fine Pitch · mm
Millimeter Ruler
1 mm & 5 mm hardware scale
Top & Bottom
Horizontal Ruler
Wide spans & CSS pixel (px) scale
Left & Right
Vertical Ruler
Upright height & mobile portrait
Related Editorial Guides
Deep-dive walkthroughs and conversion charts for this ruler mode.
Photo Measurement FAQ
Questions About Measuring Photos & Screenshots
Are uploaded photos or Ctrl+V images sent to any server?
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No. Image decoding, zoom/opacity controls, reference line math, and annotated PNG canvas export all execute locally inside your browser tab.
How accurate is two-point photo reference calibration?
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On flat overhead photos with the reference object in the same focus plane, errors are typically within 1–2 pixels across the span. Lens barrel distortion or angled shots reduce accuracy toward corners.
Can I measure width and height of rectangular UI elements?
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Yes. Toggle Bounding Boxes or ΔX/ΔY guides to read simultaneous horizontal and vertical dimensions in CSS pixels, mm, cm, or fractional inches.
What image formats work with Online Ruler Plus?
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Standard browser image formats including PNG, JPEG, WebP, GIF, and SVG files, plus direct clipboard bitmap screenshots via Ctrl+V or Cmd+V.