design tool
A0 poster checker
Drop the file you are about to send to the print shop. It is opened in this page, drawn with the trim, bleed and keep-clear margins on top of the artwork, and every check that matters for a large board is reported in words next to it: the density of each placed image, whether the fonts are embedded, and whether the smallest type still reads from a metre away.
Runs on your device. Nothing is uploaded.
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How to use it
- 1
Drop the file
A PDF opens with its page boxes, fonts and placed images intact. A JPEG or PNG is checked as a flat image against the sheet size you pick.
- 2
Pick the sheet you are printing at
The default is the size set in the file. Choose A0 portrait to see what happens when a smaller page is blown up to a board.
- 3
Read the checks and tap one
Each line says Pass, Check, Fix or Note in words. Tapping a line turns on the matching overlay so you can see the problem on the artwork.
- 4
Adjust the printer's numbers if needed
Bleed, keep-clear margin, reading distance and the smallest type allowed all live in Advanced options, with sensible defaults for a poster.
- 5
Send the report
Copy the report and paste it into the email to the print shop, so the conversation starts from the same numbers you are looking at.
Why the overlays are drawn on the artwork
A list of warnings tells you a margin is tight. Seeing the margin drawn on your own poster tells you which line of text is the problem. The trim is the solid outline, the bleed sits just outside it and the keep-clear margin just inside. On a full A0 sheet those three lines are two or three millimetres apart, which is barely a pixel on screen, so the corner is repeated magnified underneath. Low resolution images get a box and their density printed on them, and type below the readable size gets underlined.
The density a poster actually needs
Normal eyesight resolves about one arcminute of detail, and reproducing detail that fine takes two pixels across it. That works out at roughly 300 pixels per inch at arm's length and about 175 at a metre, which is where a poster is read from. Below half that figure detail is not merely wasted, it is gone. Those numbers agree with what large format printers publish, which is commonly 150 pixels per inch as a minimum for posters and 300 for anything held in the hand.
Type size and viewing distance
A capital letter reads comfortably when it is about one two hundredth of the viewing distance tall. At a metre that is five millimetres, which is roughly twenty points. Poster design guides published for academic conferences land in the same place, recommending body text no smaller than twenty eight points for a board read from four or five feet. The checker measures every text run in the file, scales it to the sheet you chose and lists the ones that fall short.
What a browser cannot check
Ink coverage, colour accuracy and overprint behaviour all depend on the press profile, which is not something a web page can hold. The tool reports whether an output intent is set, whether CMYK is declared and whether spot colours or a transparency group are present, then leaves the judgement to the printer. Treat it as a size, resolution and typography check, and let the shop do the colour proof.
Limits
- One page at a time. A multi-page PDF gets a page picker in Advanced options.
- Density is measured on the images the page places, not on how sharp the photographs are.
- It reads the trim box if the file has one, and falls back to the media box if not.
- It cannot measure total ink coverage or proof colour, because a browser has no press profile.
What it does not do
- It does not fix anything. It tells you what to change and where.
- It does not convert RGB to CMYK or flatten transparency.
- It does not upload the file, so it cannot forward anything to a printer for you.
Questions people ask
What pixel size should an A0 poster be?
About 5,800 by 8,200 pixels if you want every detail the eye can separate at a metre, which is 175 pixels per inch across 841 by 1189 millimetres. Half of that, around 2,900 by 4,100, is the point below which detail starts genuinely disappearing rather than merely going unseen. Most conference boards sit somewhere between the two.
Is 300 DPI needed for a poster?
Only if somebody will read it from arm's length. Three hundred pixels per inch is the figure for work held in the hand, and it comes from the same arcminute calculation applied at thirty centimetres. At a metre the equivalent number is about 175, and large format printers commonly publish 150 as their minimum for posters.
How much bleed does a poster need?
Three millimetres in the United Kingdom and an eighth of an inch in the United States, which are close enough to be the same number. Published price lists put posters in the same bleed band as flyers and banners, so there is no special larger figure for large format. The tool defaults to three and you can change it in Advanced options.
Why does it say my fonts are not embedded?
Because the PDF names a font but does not carry the outlines, which happens with the fourteen standard fonts that every reader is assumed to have. A press without that exact font substitutes another and the layout shifts. Re-export with fonts embedded, or convert the type to outlines, then check the file again.
It found a low resolution image but the poster looks fine on screen.
Screen is about a tenth of the size. An image placed four hundred millimetres wide on an A0 board carries the same pixels whether you view it at that size or at a quarter of it, and only the print reveals the difference. The tool reports the density the image lands at on the sheet you chose, which is the number that matters.
Can I check a page other than the first?
Yes. If the PDF has more than one page, a page picker appears in Advanced options and the whole report is rerun for the page you choose. Each page is checked on its own, because a cover and an inside spread can have different sizes, different bleed and different problems.
Is my file uploaded anywhere?
No. The PDF is parsed and rendered by code running in this page, and no network request is made after the page loads. That matters for unpublished research and for artwork under embargo, which is most of what gets checked before a conference. Nothing is stored and nothing leaves the device.
Build a board at the right size
Take what you made here into posters.
Create a poster with OneCraftRelated tools
- DPI calculatorEnter a pixel size and a print size and see the sheet drawn at real proportions, the area your file covers sharply, and a plain verdict on whether it will do.
- Aspect ratio calculatorType a size and see your shape drawn against any target: the bars if you fit it whole, the crop if you fill it. Presets for print, screen and social.
- Colour converterPick a colour on a live OKLCH plane and read it in nine notations at once, with the sRGB gamut boundary drawn and the contrast on white and black shown.
- Text diffCompare two versions line by line and word by word, with side by side or one column view. Runs in your browser, so a draft contract never leaves your machine.
- Contrast checkerSet a text colour and a background and read the WCAG ratio on a live specimen, with a pass or fail attached to every size from 30px down to 13px.
- Palette extractorCluster a photograph in CIE Lab and get the colours it is made of, each with its share of the pixels and a suggested design role. Runs in your browser.
Background reading: the question page on this.
Sources
Written and checked by the OneCraft team. Last checked .