Resize any photo to 3024 × 4032 pixels

Every resize between two different aspect ratios throws something away. The only question is what. A 3:4 target frame and a 4:3 landscape source disagree by a factor of nearly two in shape, and no amount of cleverness reconciles that without either losing image or adding blank space.

Crop to fill scales your photo until it covers the frame in both directions, then trims whatever hangs over the edges. Proportions are preserved exactly, so faces stay the right shape, but the composition changes. A subject near the left edge of a landscape photo may simply not be in the result. This is the default here because it is what produces a file that looks like it was shot in that frame.

Fit whole photo scales until the entire image is inside the frame, then fills the remainder with white. Nothing is lost from the picture, but the result has visible bands, and those bands are part of the file: anything reading the image afterwards sees a 3024 × 4032 photo with white edges, not a smaller photo with a note attached.

There is a third option this tool deliberately does not offer, which is stretching to fill. It keeps everything and fills the frame, at the cost of distorting every proportion in the image. On anything containing a face or a straight line it is immediately obvious, and it is the single most common reason a resized photo looks wrong without the viewer being able to say why.

Working out sizes yourself

The arithmetic behind the frame is worth having, because it makes the tradeoffs concrete. 3024 × 4032 is 12,192,768 pixels. The aspect ratio reduces to 3:4 exactly, since 3024 divided by 3 is 1008 and 4032 divided by 4 is also 1008, which is why the frame is a clean multiple rather than an awkward approximation.

For a source photo at 4032 × 3024, the landscape version of the same frame, cropping to fill scales by a factor of 4032 divided by 3024, or about 1.33, and then loses roughly 44 per cent of the width. For a 16:9 source it is worse: about 58 per cent of the width goes. If the subject of the photo is not near the centre, crop to fill on a wide source is usually the wrong choice, and it is worth reframing the original first.

Checking what you have before you start

The size of a photo is not something to guess at, and every platform makes it visible without a tool. On macOS, select the file and press the space bar; the preview names the pixel dimensions. On Windows, the Details tab of the file properties dialog does the same. On iOS the Photos app shows them under the info panel, and on Android under the details view of the image.

That number decides which mode is right before you upload anything here. A source already at 3:4, which many phone stills are, loses nothing to either mode: and cropping is simply a scale. A 4:3 landscape source loses roughly 44 per cent of its width to a crop. A 16:9 frame loses about 58 per cent. Anything wider than that is usually better reframed in a photo editor first, where you can choose which part survives, than centre-cropped by a tool that has to guess.

Where the extra pixels come from

Scaling up is interpolation: the browser fills the new pixels by reading the ones around them. It is good at it, and the canvas here uses high-quality smoothing, but interpolation cannot recover detail that was never recorded. The practical rule is to treat a factor of two as the limit of what looks natural. A 1512-pixel-wide source doubled to 3024 holds up. A 756-pixel-wide source quadrupled does not; edges go soft and any existing JPEG artefacts get magnified along with everything else.

This matters more than it sounds because of where photos come from. A picture that has been through a messaging app has usually been resized down and re-compressed once already, and enlarging that copy magnifies both losses. If the original is still on the device that took it, use that one.

Print and screen

At 300 dpi, the standard for photographic printing, 3024 × 4032 gives a print of about 10 by 13.4 inches. At 150 dpi, adequate for something viewed at arm's length, it doubles to roughly 20 by 27 inches. On screen the frame is taller than almost any display, so it is normally seen scaled down, which is also why softness from upscaling is easy to miss until the file is opened at full size.