Email image sizes for marketing emails

Sizes by image type

Mailchimp’s legacy templates are 600 pixels wide and templates in its new builder are 660. Klaviyo sets every new template to 600, calls it an industry standard, and advises against going wider. Both tell you to upload images bigger than they display, so they look sharp on high-density screens such as Apple’s Retina displays: Mailchimp suggests 660 to 1320 pixels wide in the new builder, and Klaviyo suggests inserting images at twice the display size and scaling them down.

Keep full-width images under 2000 pixels tall, as Klaviyo advises. Mailchimp and Klaviyo both resize images to fit the block you drop them in, so a bigger upload does not break the layout; it only makes the file heavier.

File size: what to aim for

Mailchimp recommends images of 1 MB or less. Klaviyo accepts uploads up to 10 MB but also recommends 1 MB or less, since big images load slowly. We measured what real photos weigh at email sizes:

Every file stayed well under 1 MB, even a square hero at 2x. If an export comes out near 1 MB, check its pixel size before you blame the compression.

When images do not load

Microsoft says classic Outlook blocks automatic picture downloads by default, and Klaviyo notes that Outlook and Apple Mail may not show images until the reader allows them. Plan for an email that arrives with blank boxes:

• Put the offer, the headline and the button in live text and an HTML button, not inside the photo.
• Give every image alt text that says what it shows or what it is for, such as "Blue ceramic mug on an oak table" or "Shop the autumn set". How to write alt text for product images has a formula.
• Do not build the whole email as one image. With images blocked, the reader sees nothing but alt text.

Dark mode

Email apps treat dark mode in three ways, according to Litmus’s guide (updated February 2025):

• A product photo saved as JPG keeps its own background. In an app that inverts colors, the email around it can turn dark while a white packshot stays white, so it shows as a bright box. A mid-tone or colored ground sits better in both modes.
• A logo saved as a transparent PNG with dark lettering can disappear on a dark background. Litmus suggests adding a light outline or glow, or placing the logo on a solid background.
• Words set inside an image do not adapt to dark mode. Live text does.

File formats

• JPG for photos.
• PNG for graphics with words or flat color, and anything that needs a transparent background. Klaviyo says PNG displays best for images that contain text.
• GIF for animation. Both Mailchimp and Klaviyo accept it.
• WebP: Klaviyo accepts it and converts non-animated WebP to PNG. Mailchimp lists only PNG, JPG and GIF.
• RGB color only. Mailchimp warns that CMYK files do not render accurately and can break the image.
• Dots per inch do not matter on screen. Mailchimp says 72 dpi is generally enough but not required; only the pixel width and height count.

Email heroes from AI renders

1. 1Pick the approved render and crop it to the hero’s shape. For a 2:1 hero, crop a 16:9 render: Nano Banana’s 2K 16:9 file, 2752 x 1536, crops to 2752 x 1376 and scales to 1320 x 660.
2. 2GPT Image 2.5 needs sizes in multiples of 16, and neither 1320 nor 660 is one. Ask for 1536 x 768 and scale down.
3. 3Keep the headline out of the render. Set it as live text above or below the image, or over it in your email builder, so it survives blocked images, dark mode and translation. See how to get text right in AI images.
4. 4Export as JPG, check the file size, and check the product at 100% after scaling with the AI image QA checklist.

An email hero is one more crop of the campaign’s master frame. How to adapt one campaign to every ad size covers planning that frame so the email, feed and banner versions all come from one render.

Questions people also ask

What is the best width for email images?

Match the template: 600 pixels in most builders, including Klaviyo and Mailchimp’s legacy editor, or 660 in Mailchimp’s new builder. Upload full-width images at twice that, 1200 or 1320 pixels, and let the email display them at the template width.

Should email images be 72 dpi?

It makes no difference on screen. Mailchimp says 72 dpi is generally enough but not required, and Klaviyo calls 72 dpi best practice. Email apps only read the pixel width and height, so set those correctly and ignore the dpi field.

Can I use AVIF images in email?

Not in either platform we checked. Mailchimp lists PNG, JPG and GIF, and Klaviyo lists JPEG, PNG and GIF plus WebP, which it converts to PNG. Use JPG for photos.

Sources

Checked on September 24, 2026. Prices, specs and rules change; follow the links for the current versions.

1. 1.Mailchimp Help: Image recommendations for content blocks
2. 2.Mailchimp Help: Gmail is clipping my email
3. 3.Klaviyo Help Center: About email images best practices (updated 11 February 2026)
4. 4.Klaviyo Help Center: Optimal email template width reference (updated 4 August 2025)
5. 5.Microsoft Support: Block or unblock automatic picture downloads in classic Outlook email messages
6. 6.Litmus: Ultimate guide to dark mode in email (27 February 2025)
7. 7.Google AI for Developers: Nano Banana image generation (sizes by aspect ratio)
8. 8.OpenAI: Image generation guide (size options)