Design · Best practices
Email signature size and image best practices
Email signature size is two things: how big the signature looks (its width and height in pixels) and how heavy it is (the characters of HTML code and the kilobytes of its images). Get the first right and it looks good on every screen. Get the second right and it pastes without errors and loads fast.
By the Regardly team Updated 5 min read
In short,
- Keep the whole signature at most 600 px wide; 400–500 px is a comfortable default.
- Show a photo at about 80–100 px and a logo at about 40–60 px high. Upload images at twice that size for sharp screens.
- Keep each image small (tens of kilobytes, not hundreds). Use JPG for photos, PNG for logos, and skip SVG.
- Gmail allows 10,000 characters per signature, HTML included. Long disclaimers and pasted Word formatting are the usual culprits.
- Use hosted images (a link to an image online), not attachments or embedded images.
On this page
Recommended dimensions
There's no official standard, but these sizes work well across Gmail, Outlook and Apple Mail, on desktop and on phones:
| Element | Displayed size | Upload at (2×) | Format |
|---|---|---|---|
| Whole signature | max. 600 px wide (400–500 px is plenty) | n/a | HTML table |
| Headshot | 80–100 px square or round | 160–200 px | JPG |
| Logo | 40–60 px high, up to ~200 px wide | 2× the displayed size | PNG (or JPG) |
| Social icons | 16–24 px | 32–48 px | PNG |
| Banner | up to 600 × 100–150 px | 1200 × 200–300 px | JPG or PNG |
Why 600 px? Email layouts have used it as a safe maximum for years: it fits the reading pane in desktop apps and scales down cleanly on phones. Why upload at 2×? Phones and most laptops have high-density screens. An image shown at 100 px but uploaded at 200 px stays sharp; one uploaded at exactly 100 px looks soft. Always set the displayed width and height in the HTML, which Regardly's templates do for you.
File weight: keep images light
Every image in your signature is downloaded with every email that's opened. Heavy images make emails slow on mobile data and look sloppy when they load line by line. Aim for each image to weigh tens of kilobytes; a headshot or logo rarely needs more than about 50 KB.
- Photos: JPG at around 75–85% quality is the best trade-off. Regardly compresses uploaded photos in your browser automatically.
- Logos: PNG keeps edges crisp and supports transparency.
- SVG: avoid it. Gmail and Outlook on Windows don't reliably show SVG images in email.
- GIF: animated GIFs work in most apps, but classic Outlook for Windows shows only the first frame. Make sure that frame works on its own.
Hosted images vs attachments and embedded images
There are three ways an image can end up in an email signature. Only one of them behaves well everywhere:
| Method | How it works | Downsides |
|---|---|---|
| Hosted (recommended) | The signature links to an image stored online | Shows only when the mail app loads images |
| Attached (CID) | The image is sent as a hidden attachment with every email | Paperclip icons, “attachments” in every reply, bigger emails |
| Embedded (base64) | The image is written into the HTML as code | Huge HTML, blows past Gmail's limit, blocked or stripped by many apps |
Regardly hosts the photo and logo you upload, for free, so the copied signature contains a short image link instead of the image itself. That keeps your signature small and avoids attachment clutter. Classic Outlook for Windows sometimes converts pasted images into attachments anyway; the classic Outlook guide covers the fix.
Gmail's 10,000-character limit
Gmail refuses signatures longer than 10,000 characters with the message that the signature is too long. That limit counts the HTML code, not just the text you see, so a signature that looks short can still be too long. Common causes:
- Pasting from Word, Google Docs or a website, which adds lots of hidden formatting.
- Long legal disclaimers or confidentiality notices.
- Embedded (base64) images.
- Many social icons, each with its own link and image code.
Regardly's copy button produces compact, cleaned-up HTML and warns you when a signature goes over Gmail's limit, so you can shorten the disclaimer or drop a block before Gmail refuses it.
Dark mode, blocked images and alt text
Many people read email in dark mode, and some mail apps block images until the reader allows them. Two habits make your signature hold up either way:
- Test your logo on dark. A dark logo on a transparent background can disappear on a dark screen. Use a version with a light outline or a subtle background, or a logo that works on both.
- Write alt text. If images are blocked, the alt text is what people see. Use your company name for the logo and your name for the photo. For a banner, write the message itself, such as “Webinar 12 March: register”.
- Keep the essentials as text. Name, phone number and website should be real text, never part of an image, so they stay readable, searchable and clickable.
Make it work on phones
A large share of email is read on a phone, so check how your signature looks on a narrow screen. Prefer a layout that's at most 600 px wide and doesn't rely on side-by-side columns that get squeezed; the Compact and Minimal templates are built for that. Use text of at least 13–14 px, give tap targets some room, and remember that phone apps often have their own signature setting (see the iPhone and Android guides).
Checklist before you paste
- Total width at most 600 px.
- Photo around 80–100 px, logo around 40–60 px high, both uploaded at 2×.
- Every image tens of kilobytes, JPG or PNG, no SVG.
- Images hosted online, not attached or embedded.
- Under 10,000 characters of HTML if you use Gmail.
- Alt text on every image; contact details as real text.
- Tested on a phone, in dark mode, and with images off.
Ready? Make your signature with these defaults built in, then follow the install guide for your mail app.
FAQ
Frequently asked questions
What is the best size for an email signature?
Keep it at most 600 pixels wide; 400–500 pixels is a comfortable default. Show a photo at about 80–100 pixels and a logo at about 40–60 pixels high, uploaded at twice that size.
How many characters can a Gmail signature have?
10,000, and that includes all the HTML code, not just the visible text. Long disclaimers, pasted Word formatting and embedded images are the usual reasons a signature is too long.
Why is my signature logo blurry?
It was probably uploaded at exactly the displayed size. Upload it at twice the size you want to show (for example 240 px wide to display at 120 px) and let the HTML scale it down.
Why do my signature images show up as attachments?
The images were embedded instead of linked. Use a signature with hosted images. In classic Outlook for Windows, follow our guide to stop it turning pasted images into attachments.