Email Signature Logo Size and Social Icons That Stay Sharp on Phones

The short answer: no law sets this, so the rule comes from mail platforms

No statute, tax rule or labour rule sets the size of an email signature logo. The numbers that matter come from the mail platforms themselves and from the people who build signature tools. That makes the rule practical rather than legal. You are aiming for an image that looks clean in the mail app your recipients actually use, and that does not slow the email or push the message off the screen.

Google's Gmail Help pages are the most authoritative source for Gmail. Google recommends a signature image that is 70 to 100 pixels high and 300 to 400 pixels wide, and sets a maximum of 100 pixels high by 1,000 pixels wide. That maximum is a ceiling, not a target. A logo that fills the ceiling will look too big on a phone.

Other guidance is more specific about logos. Mailmodo's 2026 guide describes a standard square logo of 100 by 100 pixels, with 64 by 64 pixels as a compact alternative. HubSpot's 2026 image guide sets a logo maximum of 150 by 50 pixels. Signkit's 2026 guide suggests a display width of 150 to 300 pixels and a file exported at double that size. These sources disagree on the exact logo box, so the sensible approach is to pick a shape that suits your logo and stay inside the Gmail limits.

How the figure is worked out, step by step

1. Start with the display size, not the file size. Decide how wide and how tall the logo should look in the signature. For a horizontal logo, a width of 150 to 200 pixels and a height of no more than 50 to 80 pixels fits most layouts.

2. Keep the whole signature block inside the width Google recommends. Google's 300 to 400 pixel range is the safe zone for the image itself, and the full block should stay near 320 to 400 pixels so it reads on a narrow phone screen.

3. Export the logo at twice the display size. A logo shown at 160 by 50 pixels should be saved as a 320 by 100 pixel PNG. The extra pixels keep edges sharp on high-density screens, which most current phones have. Signkit's 2026 guide describes this 2x method for logos.

4. Check the height against Google's 100 pixel ceiling. The exported file must not exceed 100 pixels high, so the 2x export sets a practical cap of about 50 pixels for the display height.

5. Compress the file. Vendors give different limits. Exclaimer's guidance is under 15 KB for Gmail, HubSpot suggests under 15 to 20 KB, and maileditor's guide suggests keeping a logo below 30 KB and all signature images together below 100 KB. A logo under 20 KB is a safe target that fits all of these.

6. Use PNG for logos with flat colours and transparent backgrounds. JPEG is acceptable for photos, but it has no transparency, so a logo on a coloured background will show a box.

Worked example: a horizontal logo and four social icons

Suppose your company logo is a wide wordmark with a clear background. You want it to look about 160 pixels wide on a phone. Your signature block is designed at 360 pixels wide. You also want four social icons for LinkedIn, Facebook, Instagram and a website link.

The 320 by 100 pixel logo sits at the Gmail maximum height. The 24 pixel icons match the size Exclaimer's signature handbook suggests for standard desktop signatures, and maileditor's 2026 guide puts social icons between 20 and 28 pixels. Keep all four icons the same size so the row looks tidy. Put the icons under the name and job title, not beside the logo, so the signature stacks cleanly on a narrow screen.

Then run the phone check described below. If the logo looks heavy on a phone, reduce the display width to 140 pixels and keep the 2x export. Do not solve a heavy look by uploading a large file and letting the mail app shrink it. Gmail's own help says to resize the image before upload.

The phone check: what to look at before daily use

Test on an actual phone, not by shrinking a browser window. Send a message from your desktop account to a personal phone account, and open it in the Gmail app on Android and in the native Mail app on iPhone. Check these points:

• The logo is sharp, with no fuzzy edges or a white box around it.
• The signature block does not push the message text off the first screen.
• Each social icon opens the right company profile when tapped.
• The phone and web addresses are tappable text, not just pictures.
• The image loads when you open the email, rather than showing a broken placeholder.

Outlook needs a separate check. Microsoft's own support guidance shows how to build a signature block with a photo and social icons in desktop and web Outlook. WiseStamp's guide, updated in August 2026, states that adding social icons or images is not currently possible in the Outlook Android or iOS apps. MySignature's guide says Outlook for iOS supports HTML signatures, so a signature built on desktop can be pasted into the phone app. Build the signature on desktop, paste it into the phone app, then send a test. Do not expect to add icons inside the phone app itself.

Cases that change the answer

The right size depends on the mail platform and the device your recipients use. Several cases change the answer.

• Gmail accounts. Google's ceiling of 100 pixels high and 1,000 pixels wide applies. Keep the image within the recommended 300 to 400 pixel width, even if your logo is larger.
• Outlook on phones. Images added in the phone app are not available, so the signature must be built on desktop or on the web and pasted across.
• Apple Mail and other clients. Exclaimer's guidance for Apple Mail involves building the icons in an HTML file, copying the rendered output, and pasting it into the signature settings. Test the result with an email sent to Gmail, Outlook and a phone inbox.
• Stacked or square logos. A square logo of 100 by 100 pixels, as Mailmodo suggests, takes more height than a wordmark. A stacked logo should be shown smaller, around 64 to 80 pixels high, to keep the signature short.
• Long signatures and disclaimers. Banners and legal notices add height. Some tools cap the length of a signature by character count. Gmail allows 10,000 characters, and Outlook allows 5,000 according to a 2026 comparison guide from Tabular. Long disclaimers can hit these limits before the image does.
• Reply chains. Recipients who read long threads on a phone scroll past a tall signature many times. A shorter block is kinder to them.

Common mistakes

• Uploading a 2,000 pixel photograph and letting the mail app shrink it. The file is heavy, and the result is often blurry.
• Using a JPEG logo on a dark background, which leaves a white box.
• Setting icons at 48 pixels because they look fine on a desktop monitor, then finding them too large on a phone.
• Making every icon a different size, which makes the row look uneven.
• Testing only in the account owner's own mail app, and missing how recipients in other apps see it.
• Adding too many social icons. Show only the main networks that the company uses and keeps active.

Limits of this approach

A signature cannot replace a well-designed email. Images are often blocked by default in some mail apps until the recipient chooses to load them, so the signature must still work as plain text with a name, a role and a phone number. Dimensions also vary by device, so the phone check is the only real test. Figures in this guide are starting points, and the best size for your logo is the one that looks right on the phones your recipients use.

What to agree on before rollout

No legal or tax rule governs signature images, so no statutory check applies here. The decisions are internal. Agree on one master design, one logo file, and one set of icon links, then decide who maintains them when a platform changes or a social profile moves. If the signature includes a legal disclaimer, ask your legal adviser to confirm the wording, because that is a matter for your lawyer rather than a design choice. Keep one person responsible for updating the signature across the team, so older versions do not stay in circulation.

Many businesses also spend routine staff time on signature requests, template updates and logo swaps. Employers can take this kind of routine work off their people by using AI workers that keep a signature template in sync with approved details, update contact fields from the HR or payroll record, and log each change for review. A person still approves the design, checks the legal wording and signs off the final version.