Digitaland Advertising Blog

This page is for the designers, developers and producers who build the 300×250 banner, and the ad ops teams who traffic it. It puts the specs from each platform on one page: dimensions, file weights, backup rules and animation limits. Then it covers how to design at this size, four layouts that work, and the mistakes that get a medium rectangle sent back.

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What is the 300×250 ad size (medium rectangle or MREC)?

The 300×250 is a fixed-size display ad, 300 pixels wide by 250 pixels tall. That’s a 6:5 ratio, close to square. Most specs call it the medium rectangle, and many teams shorten that to MREC.

Names vary by platform, which causes confusion on media plans:

• Google Ad Manager calls it a medium rectangle and lists it among its top-performing sizes.
• Google Ads lists the same 300 × 250 size as an “inline rectangle”.
• The IAB New Ad Portfolio (2017) marks 300×250 as a transition size and maps it to its flexible 1:1 “tile”.

All three mean the same slot. Google Ad Manager says it tends to have more advertiser inventory, and that it performs well inside article text or at the end of articles. For how it fits with the other standard units, see our IAB standard banner sizes guide.

300×250 banner specs by platform

Here is what each platform publishes for this size. Weights are maximums. Where a platform sets no 300×250-specific number, the general display limit is shown.

Sources: The Trade Desk creative specifications, Amazon DSP display specs, CM360 asset limits, Seattle Times creative guidelines and LiveIntent ad specs. For every other size on one page, use our banner ad specs cheat sheet.

IAB guidance: weight, files and animation for a medium rectangle

The IAB New Ad Portfolio groups ads by pixel area, counted at 2x resolution. A 300×250 lands in the same weight group as the 160×600 and the 970×90.

• Initial load: 150 KB.
• Subload: 300 KB, loaded after the page.
• Static image: 150 KB, which the IAB also applies to backup files.
• Files in the initial load: 10 at most.
• Animation: 15 seconds at most, with no looping beyond 15 seconds.
• CPU: 30% maximum per active ad.

Ad server and measurement files don’t count against these weights. Platforms set their own hard limits, so the IAB numbers are a design target, not an upload rule. If you’re over, our tips to reduce HTML5 banner size show where the kilobytes usually hide.

Backup images and static versions of a 300×250 banner

A 300×250 HTML5 ad usually ships with a static twin. Who asks for it, and where it goes, differs by platform:

• Google CM360: optional. But where HTML5 can’t run and there’s no backup, CM360 serves nothing. The backup must match the ad’s pixel size and must never go inside the ZIP.
• The Trade Desk: its hosted HTML5 system requires a static backup, uploaded separately.
• Amazon: per its technical guidelines, the ad’s own code must fall back to a static image when JavaScript is off or the ad fails to load. The static is capped at 40 KB.
• Yahoo: optional unless the format page asks, and it goes inside the ZIP.

The static version is sometimes the whole ad. LiveIntent lists 300×250 as a required email size, and email can’t run JavaScript. The Seattle Times takes 300×250 newsletter ads as JPG only. Google Ads accounts open under 90 days, or with under $9,000 lifetime spend, can’t upload HTML5 at all. The full platform breakdown is in our HTML5 backup image guide.

Your HTML5 campaign ZIP goes in. Backup images, GIFs and MP4s come out. Every size. Every platform. Free. JPGGIFMP4 Try it free

Designing for 300×250: what fits in the space

A 300×250 has room for one message, one image and one button. It does not have room for a paragraph. Our designers plan every medium rectangle around the final frame, then work backwards.

What we hold to at this size:

• One headline per frame. If it needs two lines, cut words before cutting font size.
• Logo on every frame or on the last. The viewer may only see one moment.
• A button that looks like a button. Our guide to CTAs that demand action covers wording and contrast.
• Fine print tested at 100%. Legal lines blur first when you compress.
• A visible border on white or very light backgrounds. The Trade Desk asks for a contrasting border on partly black or white creatives. The Seattle Times and LiveIntent ask for one on white.

Images inside the HTML5 can be exported at 2x for sharp screens, as long as the weight still fits. The backup stays at 300×250, unless a spec says otherwise. Amazon’s mobile medium rectangle is one such case: it requires the static at 600×500 @2x, still under 40 KB.

Pharma is the hardest case at this size, because safety information has to share 300 by 250 pixels with the message. Our pharma banner ads guide covers ISI layouts.

300×250 banner ad examples: four layouts that work

Most effective medium rectangles fall into one of four layouts. Each works as HTML5, GIF or static.

Whatever the layout, the end frame carries the campaign. It becomes the backup, the GIF’s first frame for email, and the frame a viewer sees after the animation stops. A three-frame story that ends on a strong end frame can be cut down to a static without new design work.

How to build a 300×250 banner that passes QA

This is the order our producers follow. It keeps one size from blocking a launch.

1. Collect every spec on the media plan. List the HTML5 limit, the static limit and the backup rule for each destination.
2. Set the strictest numbers as targets. Usually 150 KB initial load, 200 KB total and 40 KB static.
3. Design the end frame first. Then build the frames that lead to it.
4. Keep animation to 15 seconds. That meets the IAB guideline and the Seattle Times’ 15-second cap. Google Ads GIFs must stop by 30 seconds and run slower than 5 fps.
5. Wire the click-through to the platform’s clickTag. Amazon, for example, requires the ad to reference a clickTag variable.
6. Export the static versions. A 300×250 backup, a GIF if email or Google Ads is on the plan, and 2x files where a spec asks.
7. Package per destination. Backup beside the ZIP for Google and The Trade Desk, inside it for Yahoo.

Steps 6 and 7 are where hours disappear on a big campaign. Our free tool turns an HTML5 banner ZIP into backup images, GIFs and MP4s, so you don’t screenshot each size by hand. For GIF settings, see how to convert an HTML5 banner to GIF.

When the volume is high, the 300×250 is rarely alone. It usually ships with every other size, in every language. That is the work an HTML5 banner production company takes off your team. Our 170 LG banners in under 2 weeks is one example.

7 mistakes that get a 300×250 rejected

1. Building to the loosest spec. A 600 KB Google Ads ZIP won’t pass a 200 KB publisher limit.
2. A 2x backup where 1x is required. A 600×500 file fails CM360’s size match.
3. A 1x static where 2x is required. Amazon’s mobile medium rectangle needs 600×500.
4. A static over 40 KB. Amazon and the Seattle Times both cap it there.
5. Animation that never stops. The IAB limit is 15 seconds, with no looping past it.
6. No border on a white ad. The Trade Desk, the Seattle Times and LiveIntent all ask for one.
7. An HTML5 file sent to email. Email inventory takes JPG, PNG or GIF only.

Frequently asked questions

Sources

• IAB New Standard Ad Unit Portfolio (PDF, July 2017)
• Google Ad Manager: Supported ad sizes
• Google Ads: Uploaded display ads specifications
• Google CM360: Asset requirements
• Google CM360: Create a display creative
• Google CM360: HTML5 backup rules
• The Trade Desk Creative Specifications (PDF, March 2025)
• Amazon Ads: Desktop and mobile web static display ads
• Amazon Ads technical guidelines
• Yahoo HTML5 guidelines
• Seattle Times creative guidelines
• LiveIntent ad specs