EDM Size: The Dimensions, Weight and Rendering Rules That Actually Matter

The correct EDM size for almost every Singapore campaign is 600 pixels wide, with a total email weight under 100KB of HTML and images kept to a combined 1MB or less. Height is effectively unlimited, so stop asking about it. If you take nothing else from this article, set your template width to 600px, keep the HTML under 100KB, and design the whole thing to work when images fail to load.

That is the short answer, and it covers about 80 per cent of what people are actually asking when they search for EDM size. The remaining 20 per cent is where campaigns are won and lost: how the email reflows on a phone, what your image to text ratio does to deliverability, whether your design survives dark mode, and the uncomfortable truth that the heavily designed EDM your agency is proud of will usually be beaten by a plainer one.

This guide covers the specifications you need, the reasoning behind each one, and the trade offs that the specification sheets do not mention. It is written for Singapore marketers, where mobile share of email opens is very high and where a meaningful share of B2B recipients are still reading in Outlook on a corporate desktop, which is the worst of both worlds for a designer.

Why width is the only dimension that matters

Email has no viewport in the way a web page does. It has a preview pane, and the preview pane is narrow. Every rendering decision flows from that.

600 pixels became the standard because it fits inside the Outlook reading pane at common desktop resolutions without triggering horizontal scroll. That constraint has loosened slightly, and 640px is now defensible, but 600px remains the safe default and there is very little upside to the extra 40 pixels. Anything above 700px will be clipped or scaled in enough clients that it is not worth the risk.

Height is unconstrained. There is no maximum. What people are usually worried about when they ask about height is Gmail's message clipping, which is a file size limit, not a height limit. Gmail clips messages above roughly 102KB of HTML, showing a "View entire message" link. It is triggered by the weight of your code, not by how long your email is. A 4,000 pixel tall email with clean code will not clip. A 900 pixel tall email built by a drag and drop builder that emits bloated inline styles very well might.

This distinction matters because the fix is different. If you are clipping, you do not shorten the email, you clean the code: remove unused CSS, strip the comments that visual builders insert, cut redundant nested tables, and stop using extremely long tracking parameters on every link.

The specifications

Two of those deserve elaboration.

Serve images at double the display width. If an image displays at 600px, export it at 1200px and set the HTML width attribute to 600. On a retina screen an image exported at exactly 600px will look soft. This does add weight, which is why compression matters: run every image through a compressor and accept quality settings around 70 to 80 per cent, because the difference is invisible in an inbox and the file size difference is not.

Preheader text. Not a dimension, but it lives in the same design decision and it is routinely wasted. You get roughly 35 to 90 characters of preheader depending on the client and device. Most senders leave it defaulting to "View this email in your browser", which is the single most common piece of wasted real estate in email marketing. Write it as a second subject line.

Mobile rendering

The share of email opens on mobile in the Singapore lists we manage sits between 60 and 78 per cent, depending on whether the audience is consumer or business. B2B skews lower because of desktop Outlook. Consumer skews higher, and for anything retail or lifestyle you should design mobile first and check desktop second.

Your 600px template will be scaled down to roughly a 320px to 420px viewport. There are two ways to handle that.

Responsive. Media queries restack columns into a single column, resize fonts and enlarge buttons. This works in most modern clients, and it fails in some older Outlook builds, which ignore media queries entirely and render the desktop layout scaled down.

Fluid hybrid. Percentage widths with max width constraints and conditional comments for Outlook. More complex to build, more reliable across the awkward clients. This is what we recommend for anything with a significant B2B audience, because those are exactly the recipients on the clients that break responsive layouts.

Regardless of technique, the practical rules are the same. Use a single column. Multi column layouts are the most common cause of mobile rendering failure, and outside of a product grid there is almost never a reason for them. Keep buttons at least 44px tall with generous padding, because a thin text link is genuinely difficult to tap accurately. Do not put critical information inside an image, because if images do not load, the information does not exist. And test the first 100 pixels obsessively, since on a phone that is roughly all a recipient sees before deciding whether to keep scrolling.

Image to text ratio and deliverability

The old advice was a strict 60:40 text to image ratio. That specific number was never a documented rule at any major provider, and repeating it as gospel is one reason people build worse emails than they need to.

What is true is directionally more useful. Spam filters evaluate a large number of signals, and an email that is entirely one large image with almost no HTML text is a recognised pattern, because it was historically used to evade text based filtering. An email with a reasonable amount of real, selectable text is a more ordinary looking message.

More importantly, image heavy emails fail practically. Many corporate Outlook installations block images by default. Some mobile clients on slow connections delay them. If your entire message is an image, a meaningful share of your list opens your email and sees a blank rectangle with a red cross. In our experience that share sits somewhere between 15 and 30 per cent for B2B lists in Singapore, which is far too much of the audience to abandon.

The rule we work to is simpler than a ratio. Every email must communicate its full message with images turned off. Write the email as text first. Add images afterwards to support it. Give every image real alt text that reads as a sentence, because with images disabled the alt text becomes the copy. Never put your call to action inside an image, and build buttons in HTML and CSS rather than as image assets.

Dark mode

Roughly half of mobile users now have dark mode enabled and this is the most common source of "the email looked broken" complaints we receive.

Email clients handle dark mode in three ways. Some do nothing. Some invert the background and text colours only. Some, notably certain Outlook versions, forcibly invert almost everything, including colours you explicitly specified.

The failures are predictable. A black logo on a transparent PNG disappears against a dark background. Black text on a white content block sits on an inverted dark block and becomes black on dark grey. Buttons lose their contrast entirely. Images with white backgrounds sit as glaring white rectangles in an otherwise dark email.

The mitigations are also predictable. Use PNG logos with a subtle light stroke or a small padded background so they survive inversion. Avoid pure white and pure black, since near white such as #FAFAFA and near black such as #1A1A1A invert more gracefully. Give buttons a border in addition to a fill colour so that if the fill inverts, the shape survives. Add the meta colour scheme and supported colour schemes tags and prefers colour scheme media queries for the clients that respect them, accepting that several will not. And always test in dark mode, because it takes two minutes and it is the difference between a professional email and one that looks broken to half your list.

A common mistake we see

A common mistake we see is treating the EDM as a design deliverable. A brand invests in a beautiful template with a full width hero, a three column feature block, custom illustration and a carefully considered colour system. It looks excellent in the design file. It performs worse than a plain text email written by the founder.

In reality, heavily designed emails carry a structural disadvantage that has nothing to do with taste. Three things work against them.

First, they look like marketing. A recipient scanning an inbox categorises a banner heavy email as promotional in well under a second and skips it. A simple, mostly text email looks like correspondence and gets read.

Second, Gmail's tab sorting responds to signals that correlate with heavy design: lots of images, lots of links, complex markup. A plainer email is more likely to reach the primary inbox.

Third, and most practically, they break more. Every additional column, background image, custom font and nested table is another opportunity for a rendering failure in a client you did not test.

We have run this comparison across enough lists to be confident about the direction. When we replace a heavily designed template with a single column layout, one hero image at most, real HTML text throughout, and one clear call to action, click through rates typically improve. Not always, and the effect is smaller in consumer retail where the product image is the message, but in B2B and services it is consistent and sometimes dramatic.

This is not an argument for ugly emails. It is an argument for restraint. The best performing EDMs we produce look like a well set letter: clear hierarchy, one hero image, generous white space, brand colour used sparingly on the button, and copy that does the actual work. If you are choosing between spending your budget on template design and spending it on better copywriting, choose the copy every time.

There is a corollary worth stating plainly. If a plain email performs better, the correct response is not to keep the heavy template and blame the audience. It is to keep the plain email and reallocate the design budget to segmentation, subject line testing and the landing page the email points to, which is usually where the actual leak is.

Case study: a Singapore B2B services firm

One Singapore B2B services business we worked with sent a monthly newsletter to a list of just over 9,000 contacts. The template was three years old, built by a previous agency, and it was handsome. Full width hero image, a two column article block, a sponsor style banner and a footer with six social icons. Total HTML weight was 118KB, so Gmail was clipping it, and total image weight was 2.4MB.

We measured the baseline over four sends. Open rate averaged 19.4 per cent, click through rate on delivered was 1.1 per cent, and roughly 41 per cent of clicks came from the footer rather than the intended article links, which is usually a sign that nobody is reading the body.

We did not redesign it. We rebuilt it as a single column, 600px wide, one hero image at 600 by 260 displayed, exported at 1200px wide and compressed to 84KB, all body copy as real HTML text at 16px, one primary button with a 2px border, a written preheader instead of the default browser link, and the social icons cut to two. HTML weight came down to 41KB, so the clipping stopped, and total image weight to 190KB.

Across the following four sends, open rate moved from 19.4 per cent to 23.8 per cent, helped mostly by the preheader and by better primary inbox placement. Click through rate on delivered moved from 1.1 per cent to 3.4 per cent. Clicks attributable to the footer dropped to 9 per cent, because people were finding the actual links. Enquiries attributed to the newsletter went from an average of 2 per month to 7.

The client's first reaction was that the new email looked less impressive. Their second reaction, about six weeks later, was to ask why nobody had told them earlier.

Build and testing checklist

Test in at least these environments before every send: Gmail on Android, Gmail in a desktop browser, Apple Mail on iOS in both light and dark mode, and Outlook on Windows. Those four cover the overwhelming majority of Singapore inboxes and they are the four that fail differently from one another. Send yourself a live test rather than relying only on a preview tool, because preview renderings and real clients diverge more often than you would like.

Field Notes

• Across the Singapore lists we manage, mobile opens sit between 60 and 78 per cent. B2B lists cluster near the bottom of that band, consumer lists near the top. Anyone designing for a desktop preview is designing for a minority of their audience.
• When we audit an underperforming EDM programme, HTML weight above 102KB is present in roughly a third of cases. Gmail clipping is invisible to the sender, so it goes undiagnosed for months, and the fix takes an afternoon.
• Rewriting a default preheader into a genuine second subject line has produced open rate movements of 2 to 5 percentage points in our sends. It is the highest return single change available in email, and it costs nothing.
• We recommend a total image weight budget of 600KB and a hard ceiling of 1MB. Emails we have inherited routinely sit between 2MB and 4MB, which on a mobile connection means the recipient has closed the message before the hero has drawn.
• Simplifying a heavy template to a single column with real HTML text has, in our accounts, moved click through rate on delivered by between 1 and 2.5 percentage points. The effect is largest in B2B and services and smallest in fashion retail.
• A properly built, tested responsive EDM template is typically a 2 to 3 week piece of work and sits in the SGD 2,000 to SGD 6,000 range in this market. Templates quoted below SGD 1,200 are usually a repurposed builder theme, which is fine if you know that is what you are buying.

Frequently asked questions

What is the standard EDM size in pixels? 600 pixels wide is the standard, with 640px as an acceptable maximum. Keep the content itself to 560px to 580px so there is padding at the edges. There is no standard height, since emails scroll freely, and the thing people mistake for a height limit is Gmail's 102KB file size clipping, which is about code weight rather than length.

Why is my email getting cut off in Gmail? Your HTML has exceeded roughly 102KB. This is almost always caused by builder generated code, unused CSS, deeply nested tables, or very long tracking parameters on every link. Shortening the email rarely helps. Cleaning the code does. Aim for under 60KB and you will have comfortable margin.

Should I design my EDM for mobile or desktop first? Mobile, for nearly every Singapore list. Design a single column layout at 600px that reflows cleanly to a phone, then confirm it holds up on desktop Outlook. If your audience is heavily B2B, use a fluid hybrid build rather than pure media queries, because some Outlook builds ignore media queries and will render your desktop layout scaled down.

Does the image to text ratio really affect deliverability? Not as a fixed rule, and the 60:40 figure that circulates has no authoritative source. What is real is that an email consisting almost entirely of one large image with no HTML text is a recognised pattern and a practical failure, because image blocking is common. Write the email so it works completely with images disabled and the ratio takes care of itself.

How heavy should my images be? Keep total image weight under 600KB where you can and under 1MB always. Export at double the display width for retina screens, then compress at 70 to 80 per cent quality. If your hero alone is over 400KB, it is not compressed. Strong product imagery is worth the effort, which is why product photography and export discipline should be part of the same conversation.

Where to go from here

Start with the three specifications that fix most problems: 600px wide, under 60KB of HTML, and a design that works with images off. Then write a real preheader, cut to a single column, build your buttons in HTML, and test in dark mode. Those changes take a day and they will do more for your results than a new template.

After that, the constraint moves. Once the email renders correctly everywhere, performance is decided by the list, the segmentation, the subject line and the copy, which is where we would spend the next round of effort rather than on more design.

Email works best when it is not doing the job alone. Our team plans EDM programmes as part of a wider content programme so that the email, the landing page and the search content are all telling the same story. If the landing page behind the button is the weak link, that is a website design problem rather than an email one, and it is usually the first thing we fix.

For businesses building an audience to email in the first place, our SEO services grow the organic traffic that feeds list sign ups, pay per click fills the top of the funnel faster, and ongoing social media content creation keeps the audience warm between sends. If you want the wider view of how these fit together, our guide to choosing a content marketing agency for SEO sets out what good looks like, and a full digital marketing plan is where most of our clients end up.

Want an EDM programme that renders correctly and actually converts? Talk to us about content marketing and we will start by auditing your current template and your last six sends, or get in touch and forward us the email that is not working.

Natasha Tan

Natasha Tan is the founder of Digital Marketing Singapore, a full-service SEO and digital marketing agency based in Singapore. With hands-on experience across SEO, paid media, and content strategy, she works directly with Singapore businesses to build organic visibility and generate consistent leads. Natasha specialises in the Singapore market — including local search behaviour, PDPA compliance, and government grant navigation for SMEs.