How are screen resolutions measured?

The question of how are screen resolutions measured has a surprisingly simple answer

Thursday, 27 October, 2022

In recent years, few technologies have evolved and splintered quite as much as display screens.

From smartphones and tablets to TVs and monitors, the digital world relies on screens to function.

Yet those screens come in a bewildering array of formats.

Smartphones alone offer different height-to-width ratios, alongside folding displays or twin screens.

Screen display types include LCD, LED and OLED, while resolutions range from standard or high definition to 4K and even 8K.

Yet despite this diversity, the question of how are screen resolutions measured is answered in the same way. And it all comes down to dots…

Pixel perfect

A pixel is the smallest form of digital visual output.

It’s one dot on a screen, surrounded by millions of others, each changing colour individually to produce a composite picture.

The number of dots in each horizontal row, multiplied by the number of rows, gives us a screen resolution.

For instance, the default for modern laptop screens and monitors is 1,920 pixels in each horizontal row, with 1,080 different rows.

On a 4K screen, there are 3,840 pixels in each of 2,160 horizontal rows, resulting in a far crisper and sharper image.

Unlike printers (where image quality is measured in dots per inch), or cameras (whose image size depends on how many pixels it contains), monitor resolutions aren’t affected by their size.

The term ‘display resolution’ is often effectively used to describe pixel quantities.

What about ratio?

In recent years, smartphone screens have become taller as manufacturers try to move away from the broadly square screens of handsets on sale a decade ago.

Today, you can buy phones with screens at aspect ratios of 16:9, 18:9, 19:9 and even 19.5:9.

This means for every nine horizontal pixels, there are anywhere between 16 and 19.5 vertical ones.

Smartphones are usually held in portrait orientation, compared to landscape TV screens and monitors, though the growth of folding smartphone screens is challenging this somewhat.

There’s nothing to suggest TV or computer screens will also become less rectangular, since the 16:9 ratio is well established and widely accepted among consumers.

A rare exception involves 32:9 ultra-widescreen computer screens for immersive gameplay, as outlined recently in our guide to choosing a gaming PC.

What about size?

When asking how are screen resolutions measured, size is something of a red herring.

A 13-inch laptop screen might have the same 4K screen resolution as a 32-inch TV set. Both should offer comparable picture quality, even if the pixels themselves are different sizes.

An image viewed at full size will occupy the same percentage of a screen, regardless of how big that screen actually is.

While pixels appear in neat rows and columns, screen sizes are usually measured diagonally between opposing corners.

A 32-inch screen typically measures 27.9 inches in width, and 15.7 inches in height.

Neil Cumins author picture


Neil is our resident tech expert. He's written guides on loads of broadband head-scratchers and is determined to solve all your technology problems!