[FAQ]

We use a lot of images in our email designs to make them visually appealing, but I’m concerned that heavy image files might be slowing down our email load times, especially for subscribers on slower internet connections or mobile devices.

What are the current best practices in 2025 for image file formats? For example, when should I use a JPG versus a PNG or a GIF? And what’s the ideal file size I should be aiming for, both for individual images and for the total weight of all images in an email?

I’m also curious about any recommended tools or techniques for optimising images effectively before uploading them.

[Jeff Bullas]

Choosing the right file format and properly optimising the size of your images is crucial for ensuring your emails load quickly, which is essential for subscriber engagement and the overall user experience.

First, let us discuss the file formats. For most situations in email, you will be choosing between JPG, PNG, and GIF. A JPG is almost always the best option for photographs and complex images that contain many colours and gradients. It provides an excellent balance between image quality and a small file size. A PNG is the ideal choice for images that require a transparent background, such as your company logo, or for simple graphics with sharp lines and a limited number of colours, like icons. A GIF should only be used for creating simple, short animations. While modern formats like WebP offer superior compression, their support across all major email clients can still be inconsistent, so JPG and PNG remain the safest choices for maximum compatibility.

Second, you need to consider the image dimensions. You should always resize your images to the actual width they will be displayed at within your email template before you upload them. For a typical single-column email, this is often around 600 to 700 pixels wide. Uploading a very large, high-resolution image and then scaling it down with code makes the email unnecessarily heavy and slows down loading time.

Third, and this is critical, is the file size. You must compress your images to keep the file size as low as possible without a major loss in visual quality. For individual images within an email, you should aim to keep each one under 200 kilobytes (KB) if possible. For the total weight of all images in a single email, a common best practice is to try and keep it under 1 megabyte (MB).

To achieve these smaller file sizes, you need to use an image compression tool. If you use software like Adobe Photoshop, you can use its “Save for Web (Legacy)” feature, which gives you precise control over quality and file size. There are also many excellent and free online tools that can do this for you, such as TinyPNG, Squoosh, or ImageOptim. These tools can significantly reduce an image’s file size often without any noticeable drop in quality.

In summary, for fast-loading emails, you should use JPGs for your photos and PNGs for graphics needing transparency. Always resize your images to the correct display width first, and then compress them to be as small as possible, aiming for under 200 KB per image and under 1 MB for the total email.

Cheers,

Jeff

[Author]

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