Size comparison

21.5 vs 24 inch: how much bigger?

A 24-inch screen is 2.2 inches wider and 1.2 inches taller than a 21.5-inch screen (5.5 cm and 3.1 cm), and it shows 25 percent more picture. Both are the usual 16:9 shape, measured on the lit picture.

21.5-inch vs 24-inch screen size comparison, drawn to scale on one centre — Drawn to scale on one centre. The dark shape is the 21.5-inch screen and the lighter shape behind it is the 24-inch screen.

21.5-inch and 24-inch 16:9 screen dimensions compared
16:9 picture	21.5 inch	24 inch	Difference
Width	18.7 in 47.6 cm	20.9 in 53.1 cm	2.2 in 5.5 cm
Height	10.5 in 26.8 cm	11.8 in 29.9 cm	1.2 in 3.1 cm
Diagonal	21.5 in 54.6 cm	24 in 61.0 cm	12% longer
Picture area	1.4 sq ft 0.127 m²	1.7 sq ft 0.159 m²	25% more

Worked from the diagonal and the 16:9 shape, so these describe the lit picture only. In portrait, swap each width and height. The outside of a cabinet is larger by the width of its frame, so use the drawing of the exact model for a recess or a tight wall.

How far away does each one read?

The larger screen fits bigger letters for the same words, so the same message reads from farther away. Each distance is the farthest point where that much text still fits at a letter height people can read, in landscape.

On the screen	21.5 inch, read from up to	24 inch, read from up to
One short line A sign or a room name	98 ft (29.7 m) capitals 3.3 in tall	109 ft (33.2 m) capitals 3.6 in tall
Three short lines One message on a slide	62 ft (18.9 m) capitals 2.1 in tall	69 ft (21.1 m) capitals 2.3 in tall
A list of eight lines A menu, a schedule or a directory	23 ft (7.1 m) capitals 0.8 in tall	26 ft (7.9 m) capitals 0.9 in tall
Pictures and video Little or no small text	Works well to 8.8 ft (2.7 m) 14 ft (4.3 m) is the limit	Works well to 9.8 ft (3.0 m) 16 ft (4.8 m) is the limit

We plan on 1 inch of capital letter height for every 30 feet of distance, assuming 20/40 vision, and a line takes 1.7 times the capital height. For pictures the rule of thumb is 10 times the picture height, with 16 times as the limit. To start from your own distance, use the viewing distance calculator.

Pixel size at the same resolution

If both screens have the same resolution, the larger one has larger pixels, so it needs a little more distance before the picture looks smooth.

Resolution	21.5 inch pixel pitch	24 inch pixel pitch	Pixels blend from
Full HD, 1920 x 1080	0.248 mm	0.277 mm	2.8 ft (0.9 m) and 3.1 ft (1.0 m)
4K, 3840 x 2160	0.124 mm	0.138 mm	1.4 ft (0.4 m) and 1.6 ft (0.5 m)

Pixels blend where one pixel takes up about one arcminute of your vision. Whether a given model is Full HD or 4K is on its own spec sheet.

Questions

How much bigger is a 24-inch screen than a 21.5-inch screen?

A 24-inch 16:9 screen is 2.2 inches (5.5 cm) wider and 1.2 inches (3.1 cm) taller than a 21.5-inch one, and it has 25 percent more picture area. The diagonal grows by 12 percent, but area grows with the square of the diagonal.

Will a 24-inch screen fit where a 21.5-inch screen fits?

Only if the space has 2.2 inches (5.5 cm) more width and 1.2 inches (3.1 cm) more height to spare, before the frame. The picture of a 24-inch screen is 20.9 x 11.8 inches; check the outline on the drawing of the exact model before you commit.

From how far away does the extra size matter?

For pictures and video our rule of thumb is 10 times the picture height: about 8.8 ft (2.7 m) for the 21.5-inch and 9.8 ft (3.0 m) for the 24-inch. If people stand farther back than the first distance, the larger screen is the safer choice.