← All posts

White bars round a PDF page on your slide

You turned the PDF into slides, dropped them into the deck, and every slide is the same: a tall strip of page in the middle with a wide band of white on either side. It does not look like a design decision. It looks like something failed.

So you searched, and every result you got was about the opposite journey — someone exporting a PowerPoint deck to PDF and finding white margins round the printed slide. Different problem, different fix, no help at all.

Nothing failed. Two rectangles of different shapes cannot be made the same shape, and no setting in any converter changes that. What you can change is which of the three ways out you take, and the arithmetic tells you which one your document qualifies for.

The two shapes, in numbers

A portrait A4 page is 210 × 297 mm. Its proportions are 1:1.414 — the whole A series is built on the square root of two, which is why folding A3 in half gives you A4 and not a different shape.

A modern PowerPoint slide is 13.333 × 7.5 inches. Its proportions are 16:9, or 1.778 the other way up.

Put the page on the slide with its proportions kept, and it can only be as tall as the slide is: 7.5 inches. At that height the page is 5.3 inches wide, on a slide 13.33 inches wide. The page covers 39% of the slide. The other 61% is the two bars, about 4 inches each.

The rest of the common cases fall out of the same sum:

They are white for a boring reason that makes it look worse than it is: the slide background is white and the page is white paper, so the edge of the page is invisible. The eye sees content jammed into a column down the middle rather than a document mounted on a board.

Neither PDF to PowerPoint nor PDF to JPG has any bearing on this. Both draw the page at the shape the page is — a picture 1240 × 1754 pixels for A4 at 150 dpi — and hand it over. A converter that made the picture 16:9 would have to invent 8 inches of paper or throw away two thirds of the page, so none of them does.

Why dragging it bigger does not work

The obvious move is to grab a corner and pull, and it fails in one of two ways depending on which corner you grab.

Keep the proportions and enlarge, and the page grows past the top and bottom of the slide. The bars narrow exactly as fast as the page runs off the edge, so by the time they are gone you are showing the middle 39% of the page and the title is outside the room.

Ignore the proportions and stretch to fill, and you have widened the page by 2.5× against its height. Letters go fat, circles become eggs, and every rule on the page is a different weight vertically than horizontally. Nobody misses it.

It is the same trade PowerPoint offers in Picture Format → Crop, where Fit keeps the proportions and leaves the bars and Fill covers the slide by pushing the overflow off the edge. There is no third button, because there is no third option.

So: change the slide, change the page, or keep the bars and mean it.

Change the slide, when the whole deck is the PDF

If every slide is going to be a page of this document, stop fighting and make the slide the shape of the page. In PowerPoint it is Design → Slide Size → Custom Slide Size, and for A4 you type 21 cm by 29.7 cm (8.27 × 11.69 inches). Google Slides has it under File → Page setup → Custom; Keynote under Document → Slide Size → Custom. If the deck already has slides in it, PowerPoint asks whether to maximise or ensure fit — ensure fit, unless you want the existing content cropped.

One consequence to weigh. A projector or a meeting-room screen is 16:9 hardware, so a portrait deck gets letterboxed whole: your page occupies a narrow column in the middle of the wall and the back row reads nothing. The bars have not gone, they have moved from your file into the room — where they are at least black rather than white. So this is the right answer for a deck people scroll through on a laptop or receive as a handout, and the wrong one for a talk.

Change the page, when it is one figure per slide

Here is the part that is genuinely counter-intuitive, and it is why "just crop the margins" advice so often makes the slide worse.

Cropping the same amount off all four sides makes a portrait page more portrait, not less. Take 25 mm off every side of A4 and you have 160 × 247 mm, which is 1:1.54 — further from a slide than the 1:1.414 you started with. Your bars got wider.

To move a tall page towards a wide one you have to take material off the top and the bottom. And the target is unforgiving: for a page 210 mm wide to be 16:9 it has to be 210 × 9 ÷ 16 = 118 mm tall. That means removing 179 mm of a 297 mm page — 60% of its height. There is no full page of text in the world with 179 mm of dead space at the head and foot, so for a whole page the answer is simply no.

For a figure, a table, a chart or a map, the answer is usually yes, because that is what you wanted on the slide anyway. A chart drawn 160 mm wide and 90 mm tall is already exactly 16:9. A table with the running header, the page number and 60 mm of white above it cropped away is often close enough that the remaining bars stop registering.

The procedure:

  1. Get the real page size, not what a viewer shows you at some zoom. Our PDF inspector reads the page dimensions out of the file in your browser, without uploading it.
  2. Decide the finished height. Width × 9 ÷ 16 for a widescreen slide, width × 3 ÷ 4 for a 4:3 one. If that number is smaller than the thing you need to show, you are not cropping to the slide — you are cropping to the figure and accepting whatever bars are left.
  3. Measure the trims. Print one page, put a ruler on it, and read off the millimetres you want gone from each side.
  4. Run Crop PDF. Four numbers, in millimetres, one per side. It moves the crop box — the window a reader displays — rather than cutting the content, so nothing is deleted and a trim that went a millimetre too far is fixed by cropping the original again rather than by starting over.
  5. Then render. Both our renderers draw the crop box and not the full sheet, so the PNG that comes out of PDF to PowerPoint is the shape you cropped to, at the pixel count that shape deserves. Crop first, render second — the other order wastes pixels on margin.

For a book scanned page by page, run the crop twice: once with pages set to odd and once with even, with the left and right figures swapped. The wide gutter is on a different side on facing pages.

Keep the bars, and make them look deliberate

The third exit is the one nobody suggests, and on a talk it is frequently the best.

A portrait A4 page on a widescreen slide leaves you two columns of about 4 inches each. That is not wasted space; that is a column wide enough for a heading, three bullets, or the one sentence you want the room to take away. Set the slide background to something dark, and the white page now reads as a document mounted on a board — its edges visible, its shape obviously intended — with your commentary alongside it.

The bars stop being a fault the moment they contain something, or the moment they are a colour that says a page is a page.

Two pages per slide, which fixes the shape and the page count together

If the deck is a long document and the pages are portrait, N-up PDF is worth thirty seconds of your time before you convert anything. Two-up puts two portrait pages side by side on one landscape sheet, and two A4 pages side by side is 420 × 297 mm — proportions of 1.414, the landscape case from the table above, which fills 80% of a 16:9 slide.

The arithmetic is nicer than it looks. Fitted to the height of the slide, each of those two pages is 5.3 inches wide — exactly the same width as a single page fitted on its own. Nothing got smaller. You halved the number of slides and cut the bars from 4 inches to 1.4.

When a free desktop tool is better

Two of them are, and both are free:

Two things the bars are not

They are not a sharpness problem. If the page also looks soft, that is a different sum with a different answer, and enlarging the picture to kill the bars is one of the things that causes it — how many dots per inch you actually need depends on how much bigger the page is on the slide than it was on the page.

They are not the only thing wrong with a deck of page images. Every slide you have just made is a picture. Nothing on it can be selected, searched, or read aloud, so a screen reader finds nothing there at all — which matters if the deck is going to a university, a public body, or anyone who has to sign off on accessibility. Handing out the original PDF alongside is the cheap fix.

The short version: work out the ratio of your page, work out the ratio of your slide, and accept that one of them has to move. If the deck is the document, move the slide. If the slide wants a figure, crop to the figure. If it is a talk, keep the bars and put something in them.

Tools this post uses: