How do you measure screen size correctly?
Short answer: measure the visible display diagonal from one corner to the opposite corner, not the bezel or chassis.
This guide gives you the exact method for TVs, monitors, and phones, plus quick checks so your measured size matches official specs.
TL;DR Measurement Rules
- Measure only the visible display area.
- Measure diagonally (corner to opposite corner), not width.
- Ignore bezels, frame, and body dimensions.
- Keep units consistent: inches or cm, not mixed.
- If result is close (for example 54.6”), manufacturers round to market size (55”).
How to Measure Screen Size Step by Step
Step 1: Identify the active display area
Find the actual lit pixel area:
- TV/monitor: edge of panel inside the bezel.
- Phone/tablet: visible display area, not full body glass.
If your screen has curved corners, measure to the outermost lit corner points.
Step 2: Measure the diagonal correctly
Use a tape measure from one visible corner to the opposite visible corner.
- Do not bend the tape away from the screen.
- Do not start from the bezel frame.
- Keep the tape flat on the panel/glass.
Step 3: Convert units (if needed)
Use:
inches = cm / 2.54cm = inches × 2.54
Example: 68.6 cm diagonal = 68.6 / 2.54 = 27.0" (a 27-inch class display).
Step 4: Verify with aspect ratio (optional but accurate)
If you know diagonal and aspect ratio, you can verify width/height:
width = diagonal × a / sqrt(a² + b²)height = diagonal × b / sqrt(a² + b²)
For a 27” 16:9 monitor:
- width ≈ 23.5”
- height ≈ 13.2”
Use our Aspect Ratio Calculator for instant checks.
TV vs Monitor vs Phone: What Changes?
| Device Type | What to Measure | Common Confusion |
|---|---|---|
| TV | Visible panel diagonal | Mixing panel size with product width |
| Monitor | Visible panel diagonal | Ultrawide width feels “bigger” at same diagonal |
| Phone | Visible display diagonal | Display size vs phone body size |
TV measurement notes
TVs are marketed by diagonal class (55”, 65”, 75”, etc.), but the actual product width depends on bezel thickness and stand design.
After measuring, validate room fit with the TV Screen Size Calculator.
You can also compare popular TV screen sizes side by side.
Monitor measurement notes
For monitors, diagonal alone is not enough. A 34” ultrawide (21:9) and a 32” 16:9 monitor can feel very different in desk depth and horizontal span.
Use the Monitor Screen Size Calculator to compare width/height before buying.
Phone measurement notes
Phone screen size is diagonal display size, not body dimensions. Two phones with 6.7” screens can have different widths because aspect ratio differs.
Use the Phone Screen Size Calculator for display vs body context.
See how different models compare: phone screen size comparisons.
Quick Conversion Table (Inch ↔ Cm)
| Inches | Centimeters |
|---|---|
| 5.5 | 13.97 |
| 6.1 | 15.49 |
| 6.7 | 17.02 |
| 11 | 27.94 |
| 13 | 33.02 |
| 24 | 60.96 |
| 27 | 68.58 |
| 32 | 81.28 |
| 43 | 109.22 |
| 55 | 139.70 |
| 65 | 165.10 |
| 75 | 190.50 |
| 85 | 215.90 |
In real-world measuring, ±0.2” to ±0.5” variation is common depending on where you place the tape.
Common Mistakes (And How to Avoid Them)
Mistake 1: Measuring width instead of diagonal
Official screen sizes are diagonal. Width-only measurement will always mismatch marketed size.
Fix: always measure corner-to-corner diagonally.
Mistake 2: Including bezel or frame
Bezel and chassis are product dimensions, not display dimensions.
Fix: start and end on visible pixels only.
Mistake 3: Mixing cm and inches in one calculation
Using cm width with inch diagonal breaks formulas.
Fix: convert first, then calculate.
Mistake 4: Ignoring aspect ratio
Same diagonal does not mean same shape or same width.
Fix: check ratio with Aspect Ratio Calculator and compare with Common Screen Sizes.
FAQ
Is screen size measured with bezels?
No. Screen size is the visible display area diagonal only.
Why do two devices with the same inches look different?
Aspect ratio changes shape. A taller ratio gives less width at the same diagonal.
Can I convert diagonal directly to width and height?
Yes, but only if aspect ratio is known (for example 16:9, 21:9, 19.5:9).
Why does my measured size differ slightly from the listed size?
Brand listings are rounded size classes, and manual measurement position can vary slightly.
Next Step: Calculate Exact Dimensions for Your Device
Use these tools: