Apple Keynote presentations default to the 4:3 aspect ratio, but that's not always the size you need. Not all displays have the same resolution, so it's good to know how to resize slides.
Here's how to change slide size in Keynote:
2. Click Standard.
3. Choose Widescreen or Custom Size. If you select the latter, you'll be given the options to name custom height and width in pixels.
You've changed the size of your presentation slides. Since Keynote didn't automatically adjust content to fit (which PowerPoint does), it's time to resize content.