When setting up Brand Indicators for Message Identification (BIMI), one of the most common questions I get is about the recommended size for the SVG logo file. It seems like a straightforward question, but the answer has two key parts: the file size in kilobytes and the image's dimensions or aspect ratio. Getting both right is crucial for your logo to display correctly in your recipients' inboxes.
First, let's talk about the data size of the file itself. The primary rule is to keep the file as small as possible. The official guidance from the BIMI Group, the organization behind the standard, is to keep your SVG file under 32 kilobytes (KB). This is a hard limit.
In my experience, you should aim to be well below this maximum. A smaller file means it can be loaded faster by email clients, providing a better user experience. Some providers, like Fastmail, even note a smaller recommendation of under 16 KB. The key takeaway is that smaller is always better, but you must not exceed 32 KB.
Image dimensions and aspect ratio
This is where things can get a little confusing. Because BIMI uses the Scalable Vector Graphics (SVG) format, the concept of a fixed pixel size isn't as relevant as it is for raster images like JPEGs or PNGs. SVGs are built with code and can scale to any size without losing clarity. As the BIMI Group states, image sizes are generally not an issue because vector images render well at any resolution.
The single most important requirement for your BIMI logo's dimensions is that it must have a perfect square aspect ratio (1:1). Your logo needs to be designed within a square canvas. Many email clients will display your logo in various shapes, often cropping it into a circle, so ensuring it's centered in a square is essential for it to look right everywhere.
While there is no strict pixel requirement, you will see some mentioned, such as Gmail's minimum of 96x96 pixels. These values typically refer to the width and height attributes within the SVG file itself. It is good practice to define these, but always ensure they are equal to maintain the square ratio.
Key technical requirements for your BIMI SVG
Beyond size and shape, your BIMI logo must adhere to a very strict set of technical specifications to be considered valid. Failing to meet these will prevent your logo from being displayed.
- Format: The image must be saved in the SVG Tiny 1.2 or SVG Portable/Secure (P/S) format. This is a restricted subset of the SVG standard designed for security and compatibility.
- Solid Background: Your logo must have a solid, non-transparent background. You cannot use an alpha channel for transparency.
- No Raster Graphics: The SVG file cannot contain any embedded bitmap images, which means the <image> element is not allowed.
- No External Links or Scripts: For security reasons, the file cannot contain any external links, scripts, or animations.
Putting it all together
To summarize, the recommended size for a BIMI SVG image isn't just one number. It's a collection of rules that ensure your logo is secure, efficient, and displays correctly across all email clients that support BIMI.
When creating your logo, focus on keeping the file size under 32 KB, designing it within a perfect square, and saving it in the specific SVG P/S format with a solid background. By following these guidelines, you can ensure your BIMI implementation is successful and that your brand gets the visibility it deserves in the inbox.
