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Paper Size Reference (A4, Letter, ISO 216)

Every A, B, C and US paper size in mm, cm and inches, pixel dimensions at 72 to 600 dpi, a scale drawing against A4 and Letter, and the √2 rule explained.

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Paper Size Reference (A4, Letter, ISO 216) is free to use as often as you like, directly from this page. It sits under Data & computing in our catalogue, alongside Photo File Size Estimator and ISO 8601 Date Formatter.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Paper Size Reference (A4, Letter, ISO 216)?

Every A, B, C and US paper size in mm, cm and inches, pixel dimensions at 72 to 600 dpi, a scale drawing against A4 and Letter, and the √2 rule explained.

When would I actually use this?

Finding out how big a thing will be before you make it: how many gigabytes an hour of footage takes, how long a file needs on the connection you have, how large a photo prints before it goes soft, what bitrate fits the budget you were given.

What is the most common mistake?

Taking the advertised connection speed as the transfer speed. A 100 Mb/s line is megabits, the file is in megabytes, and the eight-fold difference between them is where most download estimates go wrong — before overhead and contention take their own share.

How is Paper Size Reference (A4, Letter, ISO 216) different from Photo File Size Estimator?

They sit next to each other but answer different questions: Photo File Size Estimator is the one to open when you need it to estimate the pixel dimensions and JPEG, RAW and TIFF file sizes from megapixels, aspect and bit depth. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

ISO 8601 Date Formatter is the closest one after this: Turn any date, time and UTC offset into ISO 8601, RFC 3339, week/ordinal date, RFC 2822, HTTP date and Unix timestamps.

What else is worth having open alongside it?

Audio file size calculator and Print size calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Byte prefixes follow the IEC convention where a kibibyte is 1 024 bytes and a kilobyte is 1 000 — drive makers use the second, operating systems often report the first, and a disk that shrinks on arrival is that gap and nothing else. Print sizing assumes 300 dpi unless you change it.

Further reading

All guides →
ExplainerFrame Rates, Timecode, and the Drop-Frame That Drops NothingFrames = duration × rate is trivial until the rate is 29.97. Non-drop timecode then drifts exactly 3.6 seconds an hour. Drop-frame corrects it by skipping 108 frame numbers — the same 108 — but the correction is not perfect: counting every frame shows a residual of 3.6 milliseconds per hour.ExplainerHow Big Is That Audio File?Uncompressed audio size is exact arithmetic: sample rate × bit depth × channels × seconds ÷ 8. CD audio is 176,400 bytes per second. A 320 kbps MP3, by contrast, is bitrate × duration and does not depend on the sample rate at all — 2,400,000 bytes a minute whether it came from 44.1 or 48 kHz.ExplainerScreen Resolution, Pixel Density, and the Numbers Marketing UsesA diagonal plus an aspect ratio gives you width and height by Pythagoras, and the answer is not what the marketing implies: a 27-inch 21:9 has 16.2% less area than a 27-inch 16:9. Then pixels per degree, which shows the highest-PPI phone is not the sharpest thing you own.ExplainerCrop Factor: What It Changes and What It Does NotCrop factor is a ratio of sensor diagonals. It changes framing, not the lens — proved by computing field of view both ways — and it applies to the f-number as well as the focal length, which is the half most articles leave out.How-toHow to Estimate Video File Size (Bitrate x Duration)Estimate any video's file size before you export. Learn the bitrate-times-duration formula, why you divide by 8, and how resolution and frame rate change the result.ExplainerWhat Are PPI and DPI? Pixel Density for Screen and PrintPPI and DPI both measure density per inch, but one is about screens and the other about print. Learn how to compute pixel density and what Retina really means.