Banner Ad Size Calculator

The calculation itself

Aspect ratio is width divided by height, reduced by the greatest common divisor: 300×250 is 6:5, 728×90 is 364:45, 160×600 is 4:15.

How much work a size is depends on how far its ratio sits from the design you already have. The measure used here is the larger ratio divided by the smaller, so it reads the same whichever direction you convert in.

File weight is pixels times bits per pixel divided by eight, multiplied by the number of animation frames. That gives an estimate to check a design against a network's limit before the upload rejects it.

In practice

Starting from a 300×250 at 6:5: a 336×280 is also 6:5, so it is a pure scale — the same composition at 112%. A 250×250 is 1:1, a 20% shift, close enough that the artwork survives but the text needs re-setting.

A 728×90 is 8.09:1 against 1.2:1, a shift of nearly 575%. There is no scaling that turns one into the other; the leaderboard is a new piece of artwork that happens to share a brand.

On weight: 300×250 is 75,000 pixels. At 1.5 bits per pixel that is 14,062 bytes, about 13.7 KB, comfortably inside a 150 KB budget. A 970×250 billboard is 242,500 pixels, and at the same density 44.4 KB — still fine, until animation multiplies it by the frame count.

That same 970×250 can afford about 5.07 bits per pixel before hitting 150 KB. Which is to say the budget is rarely the constraint on a static banner and almost always the constraint on an animated one.

Which sizes to build first

Six units carry most display inventory: 300×250, 728×90, 160×600, 300×600, and on mobile 320×50 and 320×100. Building those covers the large majority of placements.

They are deliberately different shapes, which is the point that catches people out — a set of six is not one design exported six times. It is roughly three compositions: a rectangle, a horizontal strip and a vertical column.

Adding the rest is worth doing only once the first six are performing. A size that does not get impressions is artwork you paid for and no one saw.

Where the figure deceives

Bits per pixel is an estimate, not a measurement. Flat colour and hard edges compress well below one; photographs, gradients and noise rarely get under two, and the same nominal design can double in weight depending on how it was exported.

File weight limits are set by each network and they change. Any single figure — including the 150 KB default here — is something to check against the network you are actually running on rather than to trust.

Designing at 1x is the commonest quality mistake. High-density screens carry most impressions, and artwork authored at nominal size is visibly soft on them; author at 2x and export down, while still meeting the weight limit at the nominal size.

Safe areas are not decoration. Networks draw close buttons and attribution over the corners, and a line of text that ends up underneath one is either rejected in review or unreadable in the wild.

Acting on it

Design the hardest shape first. A 320×50 forces every message down to the few words that will fit, and everything else is easier once that version exists.

Group the standard sizes by ratio rather than by dimension, and produce one composition per group. That turns sixteen exports into three or four pieces of real work.

Check weight before the upload rather than after. An estimate that says 40 KB against a 150 KB limit means you can afford richer artwork; one that says 190 KB means the animation needs fewer frames, not more compression.

Keep the safe-area inset proportional to the shorter edge so a set of very differently shaped units stays visually consistent.