A 34-inch ultrawide sounds a lot bigger than a 27-inch monitor. It is wider, but it is about as tall, because screens are sold by the diagonal and a wider shape spends more of its diagonal going sideways. This aspect ratio calculator turns the number on the box into the width and height you actually get.
Put in a ratio, or the resolution itself, and the screen size. It works out the picture's width and height in inches and centimetres, how much picture it holds next to a 16:9 screen of the same size, and the width or height that keeps the same shape when you resize an image or a video. Every step is shown, and every figure it supplies names where it comes from.
In this guide
The aspect ratio calculator
16 for 16:9, 16 for 16:10, 21 for 21:9. You can type the resolution instead, such as 3440, and it works out the same.
9 for 16:9, 10 for 16:10. With a resolution across, put the resolution down here, such as 1440.
The number in the product name: a 27-inch monitor is 27 here.
For resizing an image or a video: the width you have, to find the height that matches.
Or the height you have, to find the width that matches.
How that is worked out, line by line
- The same shape counted in ninths16.00 : 9
- Picture width in centimetres59.8 cm
- Picture height in centimetres33.6 cm
- Picture area312 sq in
- Area against a 16:9 screen of the same size100 %
- A 16:9 screen this tall would be sold as27.0 in
On those numbers you are in the 16:9 band, which is the section below.
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Where every number here comes from
No part of this was measured on a bench here. This site works from published specifications and from what owners report, and every number below is either one you typed in or a published figure with its source named next to it.
The figures this page supplies
- Centimetres in an inch: 2.5400 cm. Exact by definition: the international yard and pound agreement of 1 July 1959 fixed the inch at 25.4 mm, as published by NIST.
- The standard widescreen shape, across: 16. ITU-R Recommendation BT.709, the HDTV standard, sets the picture aspect ratio at 16:9. It is the shape of 1080p, 1440p and 4K, and the one most monitors and TVs are sold in.
- The standard widescreen shape, down: 9. The 9 of ITU-R BT.709's 16:9.
Why each step is the step it is
- The shape as one number:
ratio_w / ratio_h. Width divided by height. Two shapes with the same number here are the same shape, whatever they are called: 16:9 is 1.78, 16:10 is 1.60, and 2560 by 1080 is 2.37. - The same shape counted in ninths:
ratio_dec * 9. The width that goes with a height of 9, which is how 16:9 and '21:9' are both written. A 3440 by 1440 panel comes out at 21.50 and a 2560 by 1080 one at 21.33, which is why the two are both sold as 21:9 and are not the same shape. - Picture width:
diag_in * ratio_w / diag_units. Screens are sold by the diagonal of the picture. The picture's width is that diagonal scaled by the width's share of the ratio's own diagonal, which is Pythagoras and nothing else. - Picture height:
diag_in * ratio_h / diag_units. The same proportion, taken down the screen instead of across it. - Picture width in centimetres:
width_in * cm_per_in. Inches times 2.54, which is exact. - Picture height in centimetres:
height_in * cm_per_in. Inches times 2.54. - Picture area:
width_in * height_in. Width times height. Two screens of the same diagonal can differ a good deal here, which is the next line. - Area against a 16:9 screen of the same size:
area_sqin / (diag_in * diag_in * ref_w * ref_h / (ref_w * ref_w + ref_h * ref_h)) * 100. The picture area divided by the area of a 16:9 picture with the same diagonal. A squarer shape holds more picture on the same diagonal and a wider one less, so a 16:10 laptop screen has about 5% more than a 16:9 one of the same size. - A 16:9 screen this tall would be sold as:
height_in * Math.sqrt(ref_w * ref_w + ref_h * ref_h) / ref_h. The diagonal of a 16:9 picture with the same height as this one. It is the fair way to compare an ultrawide with an ordinary monitor: a 34-inch ultrawide of 3440 by 1440 is about as tall as a 27-inch 16:9 screen, only wider. - Height that keeps the shape at your width:
Math.round(px_w * ratio_h / ratio_w). Your width times the ratio's height over its width, rounded to the nearest whole pixel, because an image cannot have part of a pixel. - Width that keeps the shape at your height:
Math.round(px_h * ratio_w / ratio_h). Your height times the ratio's width over its height, rounded to the nearest whole pixel.
What this cannot tell you
Every calculator has an edge, and a page that hides its edge is worse than no page at all. Here is this one's.
- It is geometry. Nothing here was measured on a real screen, and this site has never had any of these screens in its hands.
- The diagonal on the box is usually rounded: a monitor sold as 27 inches may have a picture of 26.5 or 27.2. For the exact figure, read the viewable size on the maker's specification sheet.
- A curved screen's width here is the straight line across the picture, not the length of the curve, and the bezel and stand are not counted: the desk space it takes is larger.
- A screen's pixels are assumed to be square, as they are on every current monitor, TV and laptop. Some old video formats and anamorphic footage are not, and this does not correct for them.
- Resizing rounds to whole pixels, so a shape that does not divide evenly can be off by a fraction of a pixel. Many video encoders also want even numbers; check what yours asks for.
Screens on this site in that shape
These follow from the answer above and nothing else. Each heading below covers one span of results, so read the one the calculator pointed you at and ignore the rest.
4:3, 5:4, square or portrait
An older office shape, or a screen turned on its side. This site has not covered a monitor sold in this shape, so it is not going to name one. A 16:9 monitor on a stand that rotates gives you a tall portrait screen, which is the usual way to get one now.
16:10 and 3:2
A little taller than 16:9 for the same width, which is why many laptops have moved to it: more of a page or a spreadsheet fits without scrolling. The Acer Aspire 14 AI covered on this site has a 1920 by 1200 screen, which is 16:10.
Best Budget Laptops Under $800, 5 Honest Picks for 2026 covers this range in full.
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16:9
The shape of 1080p, 1440p and 4K, and of almost every monitor and TV. If you are choosing between sizes in this shape, the PPI calculator works out how sharp each one looks at your desk.
Best 1440p Gaming Monitor Under $300 (4 Honest Picks) covers this range in full.
144Hz Gaming Monitor, 5 Best Picks Compared for 2026 covers this range in full.
4K Monitor vs 1440p in 2026, 5 Picks and the Honest Call covers this range in full.
Ultrawide, sold as 21:9
About a third wider than 16:9 at the same height. Check the resolution, not the label: 2560 by 1080 and 3440 by 1440 are both sold as 21:9 and are not quite the same shape. The guide to 27 and 32-inch gaming monitors mentions one 34-inch 3440 by 1440 ultrawide, and notes that game support for the shape is not universal.
144Hz Gaming Monitor, 5 Best Picks Compared for 2026 covers this range in full.
Super ultrawide, sold as 32:9, and wider
Two 16:9 screens side by side in one panel. Nothing on this site covers a screen this wide yet, so it is not going to name one; the height figure above tells you which ordinary monitor it matches for height.
If you are comparing an ultrawide with an ordinary monitor, the line to read is the 16:9 screen this tall would be sold as. It puts both on the same footing, which the diagonal on the box does not. For how sharp either will look from your chair, take the resolution and size to the PPI calculator.
Questions about the aspect ratio calculator
How do you work out a screen's width and height from its diagonal?
Scale the diagonal by each side's share of the ratio's own diagonal, which is Pythagoras and nothing else. For 16:9 the ratio's diagonal is 18.36, so a 27-inch screen is 23.5 inches wide and 13.2 inches tall, or 59.8 by 33.6 cm. A 65-inch 16:9 TV is 56.7 by 31.9 inches. The diagonal is measured across the picture, so the bezel and the stand add to the desk space a screen takes.
How much bigger is a 34-inch ultrawide than a 27-inch monitor?
Wider, not taller. A 34-inch 3440 by 1440 ultrawide is 31.4 inches wide and 13.1 tall, and a 16:9 screen that tall would be sold as 26.8 inches. The 27-inch 16:9 monitor this page opens with is 23.5 by 13.2 inches, so the two are close to the same height and the ultrawide adds width. On the same diagonal a wider shape holds less picture: the ultrawide has 83% of the area of a 34-inch 16:9 screen.
Is every 21:9 monitor the same shape?
No. 21:9 is a name, and at least two shapes are sold under it. 3440 by 1440 works out at 2.39 to 1, or 21.5:9, and 2560 by 1080 at 2.37 to 1, or 21.33:9. CTA-861, the standard that HDMI's video formats come from, lists the second as 64:27. Type the resolution rather than the name into the aspect ratio calculator and it gives the real shape.
How do I resize an image without changing its aspect ratio?
Multiply the new width by the ratio's height over its width, and round to a whole pixel. At 16:9, a width of 1920 pixels needs a height of 1080, and 1280 needs 720; the other way round, a height of 1080 needs a width of 1920. The aspect ratio calculator does both at once, and it takes a resolution as the ratio, so the size of an existing image can go straight in. A shape that does not divide evenly can be a fraction of a pixel out, and many video encoders also want even numbers.
Does a 16:10 screen show more than a 16:9 screen of the same size?
Yes, a little: on the same diagonal a squarer shape holds more picture. A 14-inch 16:10 screen is 11.9 by 7.4 inches, which is 105% of the area of a 14-inch 16:9 screen at 12.2 by 6.9. The extra is height: the 16:10 screen is a little narrower and taller, so more of a page fits without scrolling.
Sources
- ITU-R Recommendation BT.709: parameter values for the HDTV standards: Sets the 16:9 picture aspect ratio of high-definition television, which is the reference shape every comparison on this page is made against.
- CTA-861: a DTV profile for uncompressed high speed digital interfaces: The standard HDMI video formats are drawn from. It lists 4:3, 16:9, 64:27 and 256:135 as picture aspect ratios, and 64:27 (2.37) is the shape behind the 2560 by 1080 screens sold as 21:9.
- NIST: SI units, length: States that since 1 July 1959 the inch has been defined as 25.4 mm, which is the centimetre conversion used here.
- FTC: the Picture Tube Rule, 16 CFR Part 410: From 1966 until its repeal in 2018, this rule required a screen size to describe the picture you can actually see and to say so when it was measured diagonally. The diagonal of the visible picture is still how screens are sold.
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