Convexy

How to convert PNG to ICO on iPhone

ICO is the Windows icon format, and it is still what a browser looks for at /favicon.ico. It also has a set of hard size constraints that most converters quietly work around without telling you. Here they are.

The size rules, stated plainly

Apple's ICO encoder — the one Convexy uses — is stricter than the ICO container itself. It accepts square images only, and only at these exact pixel sizes:

16 · 24 · 32 · 48 · 64 · 72 · 128 · 256

Anything else — a non-square bitmap, or a square at an unlisted size like 100 or 512 — is rejected outright by the encoder. It does not resize for you; it fails and leaves a zero-byte file. So every PNG has to be snapped onto that grid before it can be written.

Here is how Convexy does it, and you should know this before you convert:

If you cap the maximum dimension in Options, Convexy picks the largest permitted size at or below your cap — so setting 100 gives you a 64px icon, because 72 and 128 do not both fit under it. The grid is the grid.

A non-square logo will not look the way you expect. Icons are square; your wordmark probably is not. Aspect-fitting a 800x200 banner into a 256x256 square gives you a small strip of artwork floating in a lot of empty space — technically correct, visually poor. Design a square version of the mark, export that as a square PNG, and convert that. This is the single most common mistake in icon production, and no converter can solve it for you.

Do you actually need an ICO in 2026?

Honestly: less than you think. Modern browsers happily take a PNG or an SVG favicon declared in a <link rel="icon"> tag, and most sites now serve a PNG at several sizes plus an SVG. ICO remains worth having for two reasons:

If you are building a website, the belt-and-braces approach is a 256px ICO at the root plus PNG and SVG icons in your link tags. If you are only ever targeting modern browsers, PNG alone is fine.

Transparency is preserved. PNG has an alpha channel and so does ICO, so a transparent background stays transparent — nothing is flattened onto white. That matters for icons, which sit on unpredictable backgrounds: a dark taskbar, a light browser tab, a coloured bookmark bar.

Start from the right source

Icons are viewed at brutally small sizes, and detail that looks fine at 256px turns to mud at 16px. If you have the logo as a vector, convert the SVG to ICO instead — it renders cleanly at the exact icon size rather than downscaling a bitmap that was drawn for a different one.

If PNG is all you have, start from the largest, cleanest version you can find. Downscaling from a big PNG is fine; upscaling a 32px PNG to a 256px icon just produces a large blurry icon.

On-device

The conversion runs locally on your iPhone or iPad with Apple's ImageIO. No upload, no account, no server — worth caring about when the file is an unreleased brand mark or a client's logo.

How to do it

  1. Start with a square PNG

    Crop or pad your artwork to a square before you begin. A non-square source gets aspect-fitted onto a transparent square canvas, which is rarely the look you want for an icon.

  2. Bring the PNG in

    Tap Browse files or pick it from Photos, or share it into Convexy from another app.

  3. Choose ICO

    ICO is offered among the formats a PNG can become. Tap it.

  4. Set a size cap only if you want a smaller icon

    By default you get the largest permitted size, normally 256x256. To force a smaller one, set a maximum dimension in Options — Convexy snaps down to the largest allowed value at or below it (16, 24, 32, 48, 64, 72, 128 or 256).

  5. Convert, then save

    Save the .ico to Files. For a website, upload it to your site root as favicon.ico, and reference PNG or SVG icons in your link tags for modern browsers.

Common questions

What sizes can an ICO actually be?

In Convexy, the image must be square and one of exactly these pixel sizes: 16, 24, 32, 48, 64, 72, 128 or 256. This is a hard constraint of Apple's ICO encoder, which rejects any other dimension outright rather than resizing for you. Convexy therefore snaps every image onto that grid — picking the largest size that fits — before writing the file.

What happens if my PNG isn't square?

It is scaled to fit — never stretched or cropped — and centred on a transparent square canvas at the chosen size. So the proportions of your artwork are preserved, but a wide logo ends up as a narrow band with transparent space above and below. For a usable icon, design a square version of the mark first.

What size should a favicon be?

256x256 is the sensible default — it is the largest ICO supports, and browsers and Windows scale down from it as needed. Historically favicons were 16x16 and 32x32; those are still requested, but starting from 256 gives the system good material to work with. Remember that whatever you draw must survive being shrunk to 16px, so keep the design simple.

Do I still need a favicon.ico file?

It is still useful. Browsers request /favicon.ico by default when nothing else is declared, and various tools and readers look only there. But modern browsers also accept PNG and SVG favicons via link tags, and most sites now ship both. ICO is the compatibility floor, not the state of the art.

Does the ICO keep my PNG's transparency?

Yes. Both formats support an alpha channel, so a transparent background stays transparent and is not flattened onto white. This is important for icons, which appear against backgrounds you do not control — dark taskbars, light tabs, coloured bookmark bars.

Should I convert from PNG or from SVG?

From SVG if you have it. A vector renders cleanly at the exact icon size, whereas a PNG has to be resampled from whatever size it happened to be. Since icons are viewed very small, that difference is visible. Use PNG when the vector simply does not exist.