How many KB should an email signature be?
Keep the images in an email signature under about 50 KB in total, and under 20 KB each. The reason is Gmail's 102 KB clipping threshold, not aesthetics — and it applies to every message you send, forever.
Short answer: keep the images in your signature under about 50 KB in total, and no single image over 20 KB. A logo alone should sit somewhere between 5 and 15 KB.
That number is not a style preference. It comes from a specific, measurable limit in Gmail, and from the fact that a signature is not sent once — it is attached to every email you will ever send.
Why 50 KB, and where the number comes from
Gmail stops rendering a message once its content passes roughly 102 KB. Past that it shows the dreaded “Message clipped — View entire message” link, and everything after the cut is hidden behind a click. Your signature sits at the bottom of the message, which means it is the first thing to disappear.
That 102 KB budget covers the HTML of the message, the quoted thread underneath it, and the encoded images. Two things make it easier to hit than people expect:
- Reply chains accumulate. By the eighth reply, the quoted history is doing most of the eating. Your signature is often repeated in each quoted block too.
- Embedded images are encoded, not attached. An image pasted directly into a signature is usually base64-encoded, which inflates it by about 33%. A 30 KB logo arrives as roughly 40 KB of message.
Leave the signature at 50 KB and a long thread still renders. Push it to 150 KB and your contact details are behind a “view entire message” link on the first reply.
Pixel size is a separate question — and people conflate the two
KB is file weight. Pixels are dimensions. A signature can be small in pixels and still heavy, if it was saved as a PNG when it should have been a JPG.
For dimensions, the rule that actually matters is that most email clients display a signature at around 300–600 px wide for the whole block, with a logo at 150–200 px. Because most screens are now high-density, export the image at 2× those numbers and set the display width in the HTML. A logo intended to show at 180 px wide should be a 360 px file with width='180' on the tag.
That doubling is exactly what pushes people over budget, which is why the compression step matters. Once the pixel dimensions are settled, put the file through compress image to 20 KB, or 50 KB if the signature is a single image containing everything.
Pick the right format — and avoid one that seems obvious
The format decides how much you can save before the file looks bad.
- JPG for photographs, headshots and anything with a gradient. It compresses smoothly and lands in single-digit KB for a small image.
- PNG for a flat logo with few colours, or when you need a transparent background. A flat two-colour logo is often smaller as a PNG than a JPG, because PNG compresses solid blocks well.
- Not WebP. This is the trap. WebP is much smaller and it is the right answer almost everywhere else on the web — but classic Outlook on Windows does not render it, and your logo becomes a broken-image icon for a large chunk of corporate recipients. Email is the one place where the older format is the correct choice.
If you have the wrong one, PNG to JPG and JPG to PNG both run in the browser.
The transparency mistake nobody catches until someone complains
A transparent PNG logo with dark lettering looks perfect while you are building the signature on a white background. In a client set to dark mode, the background behind it turns near-black and the lettering vanishes.
There is no reliable way to detect dark mode across email clients, so the practical fixes are: give the logo a solid white background instead of transparency, or use a version of the mark that reads on both. Converting the transparent PNG to JPG forces the issue — JPG has no transparency, so it flattens onto white and you see immediately what recipients will see.
A realistic budget
| Element | Sensible weight |
|---|---|
| Company logo | 5–15 KB |
| Headshot (if you use one) | 10–20 KB |
| Social icons (each) | 1–2 KB |
| Whole signature | under 50 KB |
Four social icons at 5 KB each is 20 KB of decoration — nearly half the budget for something most recipients never click. Text links cost nothing and work in every client.
How to check what yours actually weighs
Send yourself an email with the signature and nothing else. In Gmail, open the message, choose Show original, and read the size at the top. That figure is the real, encoded cost of one message — the number Gmail measures against its clipping threshold.
If it is over 100 KB, the images are the cause; text and HTML are a rounding error by comparison. Shrink each image to a target and send it again.
Everything on FileFits runs inside your browser, so the logo and headshot are never uploaded anywhere — which matters more than usual for a company mark you have been asked not to circulate.