How this calculator works
A portrait frame has a width smaller than its height, so its width divided by height is below 1. That is the opposite of the usual landscape convention, where width comes first and the decimal is above 1. Pick a ratio and one side in pixels; the other side follows from the same proportion, and the megapixel count is the two sides multiplied. The social sizes in the table are platform recommendations rather than rigid standards, and several platforms accept a range of ratios while cropping to their preferred shape. A 9:16 frame is the shape of a phone screen held upright, 4:5 is the tallest shape Instagram shows in the feed, and 2:3 matches a 4 by 6 inch print turned on its side.
Formula
height = width x ratio height / ratio width. width = height x ratio width / ratio height. total pixels = width x height. megapixels = total pixels / 1,000,000. For 9:16 the width divided by height is 0.5625; for 4:5 it is 0.8; for 2:3 it is 0.6667.
Worked example
A 9:16 story uploaded at 1080 pixels wide is 1080 x 16 / 9 = 1920 pixels tall, or 2.0736 megapixels. A 4:5 feed post that is 1080 pixels high is 1080 x 4 / 5 = 864 pixels wide, or 0.93312 megapixels. A 2:3 portrait print at 1000 pixels wide is 1000 x 3 / 2 = 1500 pixels tall, or 1.5 megapixels.
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Frequently asked questions
Why is a portrait ratio written with the width first?
The convention is always width then height, even when the frame is upright. A 9:16 frame is tall, so writing it the other way round as 16:9 would describe a landscape frame. Keep the width-first order and the numbers stay unambiguous.
Which portrait ratio is best for social media?
It depends on the placement. Stories, reels and short videos use 9:16 to fill a phone screen. In-feed posts often use 4:5 because it takes more vertical space than a square without being cropped. Pins and portrait prints commonly use 2:3.
Will a 4:5 image be cropped in a story?
Usually yes. A story canvas is 9:16, so a 4:5 image leaves space above and below, which the platform fills with background or crops. Upload the ratio the placement expects to avoid unwanted cropping.
How many pixels do I need for a sharp portrait post?
Start from the platform suggested size, such as 1080 by 1350 for a 4:5 post or 1080 by 1920 for a story, and keep the original until the final export. Uploading a much larger image and letting the platform resize it is usually safe, but a small image cannot gain detail.