Why Your Converted JPG Is Bigger Than the Original HEIC

You converted a photo library from HEIC to JPG and the folder nearly doubled in size. A 2 MB photo came out at 4 MB. Every instinct says the converter is broken, or that it did something wasteful.

It didn’t. This is the expected result, and once you understand why, you can control it precisely.

The one-sentence explanation

HEIC compresses photographs about twice as efficiently as JPEG, so storing the same picture as a JPEG simply requires more space.

You’re not gaining quality by converting. You’re paying for compatibility.

The longer version

JPEG was standardised in 1992. It’s a genuinely clever design — it throws away the fine colour detail human eyes are bad at noticing and keeps the brightness detail we’re sensitive to. For its era it was remarkable, and it’s still the reason virtually every device on earth can open a .jpg.

HEIC uses HEVC compression, which came out of video research two decades later. Video codecs face brutal constraints: they must compress enormous amounts of image data or streaming becomes impossible. That pressure produced far more sophisticated techniques — better prediction of what a block of pixels will look like based on its neighbours, variable block sizes that adapt to detail, and much smarter handling of smooth gradients like skies.

Point those techniques at a single still image and you get roughly the same picture in roughly half the bytes.

So when you convert HEIC to JPEG, you’re taking an image compressed with a modern codec and re-encoding it with a thirty-year-old one. The file grows. That’s the whole story.

Why not just keep HEIC then?

Because half the world can’t open it. Windows needs extra components. Most web upload forms reject it. Print shops, older versions of Photoshop, government portals and a great deal of business software have never heard of it.

The size increase is the toll you pay for a file that works everywhere. For most people converting a photo to attach to a form, that’s an easy trade.

Getting the size back down

The size of a JPEG isn’t fixed — it’s controlled by a quality setting, usually expressed from 0 to 100. This is the single biggest lever you have.

Quality 100 tells the encoder to preserve almost everything, including detail nobody can perceive. It produces enormous files for no visible benefit. Many converters default to 95 or higher, which is why their output balloons.

Here’s roughly what to expect from a typical 12-megapixel phone photo:

• Quality 100 — Very large files. Genuinely wasteful; the extra data is imperceptible.
• Quality 90–95 — Large. Visually indistinguishable from the original for practical purposes.
• Quality 80–85 — A good default. Typically a large size reduction versus 95, with differences almost nobody spots at normal viewing sizes.
• Quality 70–75 — Noticeably smaller. Slight softening in fine detail if you go looking at 100% zoom.
• Below 60 — Visible artefacts: blocking in smooth areas like skies, haloes around high-contrast edges.

Our HEIC converter defaults to 82 for exactly this reason. It lands close to the original file size for many photos while staying visually clean. The slider is right there if you want to go higher or lower, and every file row shows you the before-and-after size with the percentage change, so you can see immediately what your setting is costing you.

Where JPEG compression actually shows

If you’re deciding how far to push the quality down, it helps to know where JPEG breaks first. Look at these areas when comparing:

Smooth gradients — clear skies, studio backdrops, out-of-focus backgrounds. JPEG tends to produce visible banding or blotchy patches here before it damages anything else.

High-contrast edges — dark text on white, a branch against bright sky. Look for faint “ringing” or ghosting alongside the edge.

Fine repeating detail — hair, grass, fabric texture, foliage. This gets progressively smeared as quality drops.

Deep shadows — blocking artefacts often appear in dark areas first.

Photographs of people and landscapes tolerate compression well. Screenshots, diagrams and anything with sharp text tolerate it badly — for those, PNG is usually the better destination, which our JPG to PNG converter handles if you need it the other way round.

An important warning about re-converting

Every time you save a JPEG, it re-applies lossy compression. Converting a JPEG to a JPEG — or converting, editing, and saving again — degrades the image a little each round. This is generational loss, and it accumulates.

Practical consequences:

• Always keep your originals. Convert copies, not your only version.
• Convert once, at the end. If you’re editing, do the editing first and export to JPEG last.
• Don’t repeatedly re-save. Going back and forth between formats compounds the damage.

Converting from HEIC is a single generation of JPEG loss, which is fine. It’s the repeated round trips that cause visible harm.

When bigger files genuinely don’t matter

Before optimising too hard, consider whether size is actually your problem. Storage is cheap and getting cheaper. If you’re converting a dozen photos to attach to an application form, the difference between 2 MB and 4 MB is irrelevant.

Size matters when you’re converting thousands of photos, when you’re bumping against an upload limit, or when you’re emailing files to someone on a slow connection. Otherwise, leave the quality high and stop worrying about it.

A quick summary

Your JPG is bigger because JPEG is a less efficient format than HEIC — that’s a property of the formats, not a fault in the conversion. You’re trading file size for the ability to open the picture anywhere.

If the size bothers you, drop the quality setting to around 80. You’ll usually get most of the space back and won’t be able to tell the difference. Keep the HEIC originals if you have room, convert copies for sharing, and don’t convert the same file repeatedly.