📌 Origin and Definition
When we say a “55-inch TV,” it means the diagonal length of the screen is 55 inches.
Since 1 inch equals approximately 2.54 cm, a 55-inch screen is about 139.7 cm diagonally.
So why use the diagonal?
This goes back to the CRT (cathode ray tube) era.
TVs then had a 4:3 aspect ratio, and manufacturers measured screen size based on the glass tube’s diagonal.
That standard simply carried over to modern flat screens.
📏 Why not use width in centimeters?
1. Aspect ratios vary
Today’s TVs come in many formats: 16:9, 21:9, even 32:9.
If we only mention the width (e.g. 100 cm), two TVs with the same width but different heights would have very different screen areas.
→ The diagonal is a more consistent and neutral comparison metric.
2. Global standardization
The TV industry started in countries like the U.S., where the inch was the dominant unit.
This convention became an international standard over time.
3. Marketing advantage
Numbers in inches often look larger and more impressive.
For example:
“55-inch TV” sounds more substantial than “121 cm wide TV,”
even though they refer to the same product.
🤓 Fun Fact
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A 55-inch TV (16:9) has a width of about 121 cm and a height of about 68 cm.
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Smartphones, tablets, and laptops also use diagonal inches to express screen size.
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In some European countries, TV packaging also includes centimeter measurements, but inch sizes are still dominant in marketing.
🌍 What about other countries?
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🇺🇸 USA, 🇯🇵 Japan, 🇰🇷 Korea, 🇨🇳 China: Use inches and diagonal measurement.
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🇫🇷 France, 🇩🇪 Germany: May include cm for local labeling, but marketing still favors inches.
🎯 In Summary
TVs use inch-based diagonal measurements because of long-standing industry tradition.
As screen aspect ratios vary widely, the diagonal length offers a reliable comparison.
Though using centimeters is possible, inches are globally accepted, reduce confusion, and work well for marketing purposes.
Tags: TV size, inch measurement, diagonal screen, aspect ratio, display standard