Introduction

Two aspect ratios are "close" if their width-to-height proportions are numerically similar, not if their raw width and height numbers look similar. The practical way to compare them is to convert each ratio into a decimal and measure the difference. If you want a comparison that feels more proportional, use percentage difference instead of raw subtraction.

Convert Each Ratio to a Single Number

An aspect ratio such as 16:9 means 16 / 9, which is about 1.7778. A ratio such as 4:3 means 4 / 3, which is about 1.3333.

Once every ratio becomes a decimal, comparison is straightforward.

1def ratio_value(width, height):
2    return width / height
3
4print(ratio_value(16, 9))
5print(ratio_value(4, 3))

That decimal is the quantity you should compare.

Use Absolute Difference for a Simple Ranking

A simple closeness metric is the absolute difference between the decimal values.

1def aspect_distance(a_w, a_h, b_w, b_h):
2    return abs((a_w / a_h) - (b_w / b_h))
3
4print(aspect_distance(16, 9, 17, 9))
5print(aspect_distance(16, 9, 4, 3))

Smaller difference means closer aspect ratios.

This is usually enough when you just want to sort a list by similarity.

Compare Many Ratios at Once

If you have a target ratio and several candidates, rank them by that distance.

1def closest_ratios(target, candidates):
2    target_value = target[0] / target[1]
3    return sorted(
4        candidates,
5        key=lambda r: abs(target_value - (r[0] / r[1]))
6    )
7
8candidates = [(4, 3), (3, 2), (16, 10), (21, 9)]
9print(closest_ratios((16, 9), candidates))

This returns the list ordered from closest to farthest from the target.

Percentage Difference Can Be More Intuitive

Raw decimal difference is easy, but sometimes percentage difference feels more meaningful because it scales relative to the target.

1def percentage_difference(a_w, a_h, b_w, b_h):
2    a = a_w / a_h
3    b = b_w / b_h
4    return abs(a - b) / a * 100
5
6print(percentage_difference(16, 9, 17, 9))

This helps when you want to know not only which ratio is closest, but how much distortion or cropping difference to expect relative to a baseline.

Reduce Ratios First Only for Readability

Reducing 1920:1080 to 16:9 is useful for presentation, but it does not change the comparison result because both pairs represent the same proportion.

So simplification is optional mathematically. It only makes the ratios easier to read.

Visual Similarity Depends on Context Too

Two ratios can be numerically close but still matter differently depending on the application.

Examples:

• in video, small ratio changes can create visible letterboxing or cropping
• in UI design, the same difference may be acceptable if the layout is flexible
• in printing or photography, the important question may be crop loss rather than the raw ratio delta

So the metric gives you closeness, but the acceptable threshold still depends on the use case.

Common Pitfalls

• Comparing raw width and height numbers instead of comparing the width-to-height proportion.
• Forgetting that 1920:1080 and 16:9 are the same aspect ratio even though the numbers look different.
• Using decimal difference without considering whether percentage difference is a better fit for the decision.
• Assuming the numerically closest ratio is automatically acceptable for the specific design or crop requirement.
• Ignoring orientation, such as portrait versus landscape, when interpreting the result.

Summary

• Convert aspect ratios to decimal width-to-height values before comparing them.
• Use absolute difference for a simple closeness ranking.
• Use percentage difference when you want a relative sense of how far apart the ratios are.
• Simplifying ratios helps readability but does not change their mathematical comparison.
• The numeric closest ratio is only part of the decision; the use case still determines whether it is close enough.