What aspect ratio should I design mobile app screens at?

Design for a tall ratio around 19.5:9, which covers most current iPhones and flagship Android handsets, then check the layout at 16:9 and at the shortest device you support. Anything full-bleed needs a safe centre that survives cropping at both extremes.

How do I calculate an aspect ratio from two dimensions?

Divide both numbers by their greatest common divisor. 1920×1080 divided by 120 gives 16:9. This tool does it automatically and shows the simplified ratio alongside the decimal value.

What is the difference between 16:9 and 9:16?

They are the same proportion rotated. 16:9 is landscape — wider than it is tall, used for video. 9:16 is portrait, the orientation almost all full-screen phone content uses.

Does this calculator cost anything?

No. It is free and unlimited with no account needed to calculate. Signing up free lets you copy the results out.

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Aspect Ratio Calculator

Work out the missing width or height for any ratio, with the common phone and store ratios one click away.

Calculate freeSign up to copy the dimensionsNo usage limits

What do you want to work out?

Solve a missing side, or derive the ratio from two you already have.Ratio

Width (px)

Width: 1080 px
Height: 1920 px
Simplified ratio: 9:16
Decimal: 0.5625
Orientation: Portrait
Megapixels: 2.07 MP

Enter either the width or the height, pick a ratio, and the other dimension appears. It sounds trivial until you are resizing a hero image for six device classes and the arithmetic starts costing you real minutes.

Presets cover the ratios that actually come up in mobile work: 9:16 for full-screen phone art, 16:9 for landscape video, 1:1 for avatars and store tiles, plus the tall ratios modern handsets use.

What an aspect ratio actually describes

An aspect ratio is the proportional relationship between width and height, written as two numbers separated by a colon. 16:9 means that for every 16 units of width there are 9 of height — it says nothing about absolute size, which is exactly why it survives scaling. Two images at 1920×1080 and 640×360 are both 16:9 and will crop identically into the same slot.

Why phone ratios stopped being simple

Phones used to be 16:9 and that was the end of it. Now they run anywhere from 18:9 to past 21:9, and foldables change ratio mid-session. Designing to a single ratio guarantees letterboxing or cropping somewhere in the range, which is why full-bleed art needs a safe centre that survives being trimmed at both extremes.

Scaling without resampling twice

Every time an image is resized and re-encoded it loses a little detail. Work out the target dimensions first, export once from the source at that exact size, and you keep the quality you started with. Calculating the ratio after the fact — and nudging a nearly-right image into place — is how screens end up subtly soft.

How to use the aspect ratio calculator

Choose what you are solving for: a missing height, a missing width, or the ratio itself from two dimensions you already have.
In the two solve modes, pick a ratio preset and type in the dimension you know.
In “Ratio from both”, enter the width and height of an existing asset to get its simplified ratio — useful for working out what an inherited image actually is.
Read the simplified ratio, the decimal value, the orientation and the megapixel count.
Export your source asset once at those exact dimensions rather than resizing an almost-right file.

Use it with

Device Size Reference — Screen dimensions, logical points, pixel density and safe areas for current iPhones and Android handsets.
Placeholder Image Generator — Build placeholder images at any size, with your own colours, label and format.
App Store Screenshot Sizes — Required screenshot dimensions for the App Store and Google Play, with counts and limits.

Frequently asked questions

What aspect ratio should I design mobile app screens at?: Design for a tall ratio around 19.5:9, which covers most current iPhones and flagship Android handsets, then check the layout at 16:9 and at the shortest device you support. Anything full-bleed needs a safe centre that survives cropping at both extremes.
How do I calculate an aspect ratio from two dimensions?: Divide both numbers by their greatest common divisor. 1920×1080 divided by 120 gives 16:9. This tool does it automatically and shows the simplified ratio alongside the decimal value.
What is the difference between 16:9 and 9:16?: They are the same proportion rotated. 16:9 is landscape — wider than it is tall, used for video. 9:16 is portrait, the orientation almost all full-screen phone content uses.
Does this calculator cost anything?: No. It is free and unlimited with no account needed to calculate. Signing up free lets you copy the results out.