PNG vs JPG, measured
Two formats built for opposite pictures. Rather than repeat the usual rule of thumb, here are four drawn pictures written both ways, with the bytes.
The measurement
Four pictures were drawn for this note, each 1,200 × 800 pixels: a two-colour logo with a transparent surround, an interface screenshot of a table, a three-line chart, and a smooth gradient with fine grain standing in for a photograph. Each was saved as PNG with a standard zlib encoder at its highest setting, and written as JPEG by this site's precision encoder, which gives the same bytes in every browser. Similarity is this site's luma SSIM over the parts of each picture with detail in them (1.000 is identical).
| Picture | PNG | JPG q86, 4:2:0 | JPG q86, 4:4:4 | JPG q95, 4:4:4 |
|---|---|---|---|---|
| Logo, transparent surround (on white) | 16.3 KB | 18.5 KB · 0.992 | 27.3 KB · 0.992 | 37.8 KB · 0.997 |
| Interface screenshot (table of rows) | 33.4 KB | 59.5 KB · 0.997 | 68.7 KB · 0.997 | 90.1 KB · 0.999 |
| Line chart, three series | 16.1 KB | 79.3 KB · 0.996 | 107.7 KB · 0.997 | 157.2 KB · 1.000 |
| Photo-like gradient with grain | 761.3 KB | 55.0 KB · 0.992 | 83.5 KB · 0.993 | 199.5 KB · 0.996 |
Measured on 23 October 2026. 1 KB is 1,024 bytes.
What the table says
- Three of the four pictures are larger as JPG at every setting tried. The chart is five times larger at quality 86, and the PNG is exact.
- The photo-like picture is fourteen times smaller as a JPG at quality 86, with similarity 0.992. That is the case JPEG was designed for.
- 4:4:4 colour costs 15–50% more bytes than 4:2:0 at the same quality, and the brightness-only similarity barely moves: what it buys is colour detail, which shows on coloured text and thin coloured lines.
- The logo's JPG has a white box where the PNG was transparent. The size comparison is fair only once that is accepted.
The rule that follows
If it came off a screen — a logo, a screenshot, a chart, a diagram — expect the PNG to be smaller and sharper, and convert only when something demands a JPG. If it came out of a camera, convert, and expect the file to shrink by an order of magnitude. The converter on this site measures your own file both ways before you save, so you do not have to guess which kind it is.
Questions
- Is JPG or PNG better quality?
- PNG keeps every pixel exactly; JPG never quite does. Whether the difference is visible depends on the picture: on a photograph at quality 86 it rarely is, on small coloured text it often is.
- Which is smaller?
- For photographs, JPG by a wide margin — fourteen times smaller in the table above. For logos, screenshots and charts, PNG is often smaller as well as exact.
- Can a JPG be transparent?
- No. JPEG has no alpha channel, so every transparent pixel becomes a colour when a PNG is converted. That colour is the one decision this site is built around.