Keep a photo in HEIC and it takes roughly half the storage of a matching JPG. Convert that same file to JPG and the byte count usually climbs, unless extra container streams or lower quality settings tip the balance.
HEIC is smaller at equal visual quality. Apple uses HEVC intra-frame compression inside a HEIC file, which stores the same detail in roughly half the space of a baseline JPG.
Converting HEIC to JPG usually makes the file bigger. Re-encoding a modern HEVC image with JPEG's older block maths forces the encoder to spend more bytes just to preserve the same sharpness.
A converted JPG only shrinks when you drop data. Lowering the JPEG quality slider, downscaling pixel dimensions, or stripping hidden Portrait depth maps can produce a smaller JPG.
JPEG relies on Discrete Cosine Transform (DCT) maths standardized in the early nineties. It slices every photo into rigid 8x8 pixel blocks and compresses each block nearly on its own. HEIC stores an image compressed with HEVC (H.265), which groups pixels into flexible Coding Tree Units up to 64x64 pixels across and applies 35 intra-frame prediction modes. When your photo has a flat blue sky or an out-of-focus wall, HEIC describes huge regions at once instead of repeating work across hundreds of tiny squares. Do not batch-convert an archive drive from HEIC to JPG hoping to free up disk space; you will do the exact opposite.
| Feature | HEIC (HEVC Main / Main 10) | Baseline JPG (JPEG DCT) |
|---|---|---|
| Partition size | Flexible up to 64x64 pixels | Fixed 8x8 pixel blocks |
| Spatial prediction | 35 intra prediction modes | DC coefficient diff only |
| Colour depth | 8-bit or 10-bit per channel | 8-bit per channel |
| Chroma subsampling | Typically 4:2:0 on iPhone | Typically 4:2:0 |
There is no direct mathematical shortcut that turns HEVC blocks into JPEG blocks. Every converter first decodes your HEIC into an uncompressed grid of 8-bit RGB pixels in memory, then runs a fresh JPEG pass over that grid. Because JPEG's 8x8 transform is far less efficient at packing fine edges and sensor noise, matching the look of the original photo requires a high JPEG quality setting and a significantly larger file. You can see what happens on real camera roll files in our guide to measured HEIC to JPG file sizes.
Built-in system tools often make JPG look smaller by quietly cutting your photo's dimensions. In the iPhone Files app, holding down on a photo and tapping Quick Actions then Convert Image prompts you to pick Small, Medium, Large, or Actual Size. Finder on macOS shows the exact same four options under Quick Actions > Convert Image. Anything other than Actual Size throws away megapixels to push the byte count down. Always pick Actual Size unless you are deliberately shrinking a photo to get past strict upload size limits on an old web portal.
Settings > Camera > Formats > High Efficiency (introduced in iOS 11) so originals take roughly half the room on your device and in iCloud..heic file..jpg to hit a smaller byte target.Keeping your master library in HEIC and generating JPGs on demand gives you small backups and universal compatibility at the same time.
Drop a photo from your iPhone into the converter and compare the downloaded .jpg against your original .heic in Finder or File Explorer. Everything runs locally inside your browser tab, so you can test different quality levels and check the exact output size without uploading your photos anywhere.
Your photos are decoded in your own browser — open the converter and see.
First published: 26 October 2026