Aspect Ratio Converter

Converting between aspect ratios always comes down to a mismatch between Source Width / Source Height and the Target Aspect Ratio, and this calculator shows both ways to resolve it: adding bars (preserving every source pixel) or cropping (filling the frame, losing some source area). When the source is relatively wider than the target -- a 21:9 cinematic source going onto a 16:9 display, for example -- fitting the full width means adding Letterbox Bar Height above and below, while filling the frame without bars means trimming Crop Width down and keeping the full Source Height. When the source is relatively narrower than the target -- a 4:3 source going onto a 16:9 display -- fitting the full height means adding Pillarbox Bar Width on both sides, while filling the frame means trimming Crop Height down and keeping the full Source Width.

Only one of Letterbox Bar Height or Pillarbox Bar Width is ever non-zero for a given conversion, since a source can't simultaneously be both relatively wider and relatively narrower than the target. Image Retained is the share of the original pixel area the crop option keeps -- it's always 100% for the bars approach, since letterboxing and pillarboxing never discard source pixels, only add blank space around them. Pixel Loss is the flip side: the actual pixel-area difference between the source and the cropped output.