Ratio Rule

Aspect Ratio Compare & Crop

See what is cropped away, or left over, when content in one shape has to fit another.

Source ratio

The shape your content is now — 16:9 for standard widescreen video, 4:5 for a tall social post.

Source presets

Target ratio

The shape it has to end up in. Filling that frame crops the content; fitting it leaves empty bars.

Target presets

Source pixel dimensions (optional)

Optional — add the real pixel size of your content to see the crop in pixels as well as percentages.

px
px

Add real dimensions to see the crop in pixels as well as percentages.

Area cropped

55%

Fitting 16:9 content into a 4:5 frame. The source is wider than the target, so the left and right edges are cropped. 45% of the source area is kept.

Fill and crop

Target 4:5Source 16:9
  • Visible source
  • Target frame
  • Cropped away
16:9 content filling a 4:5 frame. 45% of the source is kept and 55% is cropped away.The crop is centred. Cropped and unused areas are marked with hatching as well as colour.

Details

  • Source ratio16:91.7778 decimal
  • Target ratio4:50.8 decimal
  • Source area kept45%
  • Source area cropped55%
  • DirectionLeft & rightEdges removed

Formula and assumptions

sourceRatiosourceWidth ÷ sourceHeight

targetRatiotargetWidth ÷ targetHeight

How much survives the crop

retainedFractionmin(sourceRatio ÷ targetRatio, targetRatio ÷ sourceRatio)

croppedAreaPercent(1 − retainedFraction) × 100

When the source pixel dimensions are known

croppedWidthsourceHeight × targetRatio (source wider than target)

croppedHeightsourceWidth ÷ targetRatio (source narrower than target)

Assumptions

  • All crop figures assume a centred crop, with an equal amount removed from opposite edges.
  • Percentages describe area, not a single edge.
  • The source content itself is never stretched or distorted in either mode.
  • Pixel figures are only shown when you supply real source pixel dimensions.

Questions

What is the difference between fill and fit?

Fill scales the content until it covers the target frame completely, so anything outside the frame is cropped away. Fit scales the content until all of it is visible, so unused space appears as bars on two sides. Neither changes the proportions of the content itself.

Where is the crop taken from?

These figures assume a centred crop, with an equal amount removed from opposite edges. If you crop off-centre the total amount removed is the same, but the split between the two sides changes.

Why does swapping source and target change the direction?

Cropping is not symmetrical in direction. Putting 16:9 content into a 4:5 frame removes the left and right edges. Putting 4:5 content into a 16:9 frame removes the top and bottom instead.

Do equivalent ratios give the same answer?

Yes. 16:9 and 1920:1080 describe the same proportion, so they produce identical crop figures.

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