Banner ads: the sizes that actually get bought, what fits inside each one, and six worked examples

A banner ad has to work at the size of a business card while somebody is reading something else. That constraint, rather than any theory of advertising, decides everything about it: one message, one picture, one button, and a brand mark somebody can recognise without reading it. Most banner creative fails for the same two reasons, which are trying to fit a paragraph into a space that holds nine words, and producing one size when the inventory needs five. The sizes below are the ones you will actually be asked for, and the examples are filled in so you can see how little text survives.

This page is about digital display banners. If what you need is a printed banner for a shopfront, a stand or a fence, that is a different specification and a different supplier, covered in outdoor marketing banners.

The sizes worth producing

Size	Known as	Where it runs	Words that fit
300 x 250	Medium rectangle	In article and sidebar, desktop and mobile. The most widely available slot there is	About 10 to 14
728 x 90	Leaderboard	Top and bottom of desktop pages	About 8 to 10, on one line
320 x 50	Mobile leaderboard	Anchored to the bottom of a phone screen	5 or 6, plus a small button
300 x 600	Half page	Desktop sidebar. The most generous space you will get	About 20, and room for a real image
160 x 600	Wide skyscraper	Desktop sidebar, narrow	About 8, stacked
970 x 250	Billboard	Top of desktop pages, premium placements	About 12, with a wide image

Produce the first four and you cover most of the inventory you will be served. Ad platforms also accept responsive display formats, where you supply images, headlines and descriptions and the system assembles the unit, which is the sensible default for a small advertiser and the reason to write the text as separate parts rather than as a finished picture. Check the current accepted list in whichever platform you are buying through, since each one publishes its own.

The four elements, and nothing else

• One line that names the reader or the problem. Not your company, not your category. The line has to be readable at a glance by somebody who was not looking for it.
• One image that is the thing itself. The product, the finished work, the real room. Stock photography of people in a meeting reads as an advertisement for nothing.
• One piece of proof, if there is room. A number, a named certification, a review count. In the smaller sizes this is the first thing to cut.
• One button with a verb. Get a quote, See the range, Book a slot. Learn more is the default and it asks for nothing.

Plus the brand mark, small, in a consistent position across every size, because a set of banners that each place the logo somewhere different stops reading as a campaign.

Six worked examples

Square brackets are the parts you replace. Each one is written to fit the size named, so resist adding a line.

• Local trade, 300 x 250. Headline: Boiler repairs in [Town], same week. Line two: Fixed quote before any work. Proof: [Number] reviews. Button: Get a quote. Image: a van and an engineer, photographed on a real job.
• Ecommerce product, 300 x 250. Headline: [Product] in [new colour]. Line two: Free returns, dispatched today. Button: Shop the range. Image: the product on a plain background, filling two thirds of the frame.
• B2B software, 300 x 600. Headline: [Job title]s spend [time] a week on [task]. Line two: [Product] does it in [time]. Proof: Used by [number] teams. Button: See a two minute demo. Image: one screen of the product, cropped to the part that matters.
• Professional service, 728 x 90. One line only: [Service] for [sector] businesses in [city]. Button: Book a call. No image beyond the mark, because there is no room for one that reads.
• Event, 970 x 250. Headline: [Event], [city], [date]. Line two: [Number] speakers, [number] workshops, [price] until [date]. Button: Get a ticket. Image: a wide shot of last year's room.
• App or mobile offer, 320 x 50. Five words and a button: [Benefit] in [time]. Button: Try free. Nothing else fits, and anything else you add makes the five words smaller.

The rules that come from the format

• Readable at arm's length on a phone. Export the file, look at it on your own handset, and cut whatever you have to lean in to read.
• Keep the file small. Platforms cap the weight, and a heavy animated unit that loads late is an impression nobody saw.
• If it animates, make the last frame complete. Many viewers only see the end state, so the final frame has to carry the message, the brand and the button on its own.
• Contrast over brand palette. Your brand colours have to work against a white page, a dark page and a photograph. Where they do not, the guidelines should name the alternative, which is one of the things brand guidelines exist to settle.
• The landing page repeats the words in the banner. A click that lands somewhere that does not mention the offer is a bounce you paid for.
• Two versions, one difference. Change the headline or the image, never both, or the result tells you nothing.

Where banners run and how they get bought

Display inventory is bought in three ways and the creative does not change between them. Self service through an ad platform, where you upload the sizes or supply responsive assets and the system places them. Programmatically, through a demand side platform buying across thousands of sites, which is what an agency means by display, and what one of those agencies actually does is set out in the four models of a programmatic display agency. Or directly from a publisher, which is how a trade title sells its own slots and is often the better buy in a narrow sector. Where display sits among the other places you could spend the same money is compared in paid advertising platforms.

The two numbers that tell you what to fix

Display produces a low click rate everywhere, so the absolute figure tells you little. The diagnosis comes from a pair.

• Click rate by placement. If one site or app is far below the rest, the problem is the placement rather than the creative, and the placement report is where you exclude it.
• Bounce or conversion rate after the click. A reasonable click rate and a terrible outcome after it means the banner promised something the page does not deliver.
• Together. Low clicks everywhere and a decent conversion rate from the few who click is a creative problem. Good clicks and nothing afterwards is a landing page problem. Fixing the wrong one is the usual outcome of looking at a single number.

For anything bought on reach rather than clicks, a held out region is the honest measurement, because display's main effect is on people who never click at all.

Questions about banner ads

What size banner should I make first?

300 x 250, because it is accepted in more places than anything else and it holds enough text to say something. Then 728 x 90, 320 x 50 and 300 x 600 to cover desktop and mobile properly.

How many words can a banner hold?

Between five and twenty depending on the size, including the button. The examples above are written to those limits, and the discipline is to write the offer in one sentence first and then cut it to fit.

Do banner ads still work?

They work for reminding people who already know you, for narrow placements where the audience is the site rather than a profile, and for retargeting. They work badly as a way to introduce a complicated product to a stranger, which is the use they are usually blamed for.

Should I use animation or a static image?

Static first, because it is cheaper to produce in five sizes and it cannot be half seen. Add animation when there is a sequence worth showing, and make the final frame stand alone.

What about ad blockers?

A share of the audience will not see display advertising at all, which is one argument for also buying placements inside content, such as newsletters and trade titles, where the unit is part of the page.

Who should make them?

Whoever holds your brand assets, working from a written offer. The expensive mistake is commissioning one beautiful 300 x 250 and then having somebody resize it badly into four other formats the week the campaign starts.

The banner nobody is paying for

Every unit above is a paid interruption, bought by the thousand, aimed at being noticed for a second. There is now a placement that costs nothing and carries far more weight: the two or three sentences an assistant produces when a buyer asks who to use in your category, with one company named first and a line of description against each. It is assembled from what has been published about those companies, which means no media budget reaches it. Worth reading the one that exists in your category today, with your own name kept out of the question so the answer arrives clean. AI Knows Us asks those buying questions across the main assistants and records which companies get named and what the answers were built from.