Calculate a size ratio such as height to width or length to width in simplest form, or find a missing dimension from a ratio and a side, area or diagonal.
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Size Ratio Formula
The size ratio compares total height to total width. The calculator uses the height-to-width ratio, written as height:width.
- H = total height
- W = total width
- R = numeric size ratio
- a:b = ratio entered as height:width, such as 4:3 or 16:9
- a = height part of the ratio
- b = width part of the ratio
If you enter height and width, the calculator finds the ratio by dividing height by width. The result is shown as a ratio against 1, such as 1.3333:1.
If you enter height and ratio, the calculator finds width by dividing height by the numeric ratio. If you enter width and ratio, it finds height by multiplying width by the numeric ratio.
Height and width can use different physical length units. The calculator uses consistent physical units internally and converts the missing value to the selected result unit. Pixels are image counts with no assumed DPI; they must be used together and cannot be converted to physical lengths without a specified pixel scale.
Common Width-to-Height Ratios
The display and photo conventions below are written width first. Choose Width : Height in the calculator to use them in that order; its comparison output is always height : width. Decimal values are rounded.
| Ratio | Decimal Width ÷ Height | Common Use |
|---|---|---|
| 1:1 | 1.0000 | Square images, tiles, icons |
| 4:3 | 1.3333 | Older displays, photos, slides |
| 3:2 | 1.5000 | Photography prints and sensors |
| 16:9 | 1.7778 | Widescreen video and displays |
| 21:9 | 2.3333 | Ultrawide screens |
Length Unit Conversion Reference
| Unit | Meters per Unit | Example |
|---|---|---|
| Meter | 1 | 2 m = 2 m |
| Centimeter | 0.01 | 100 cm = 1 m |
| Millimeter | 0.001 | 1000 mm = 1 m |
| Inch | 0.0254 | 12 in = 1 ft |
| Foot | 0.3048 | 3 ft = 0.9144 m |
Example Size Ratio Calculations
Example 1: Find the size ratio
You have a height of 8 inches and a width of 6 inches.
The exact height-to-width ratio is 4:3, or approximately 1.3333:1.
Example 2: Find the missing width
You have a height of 120 cm and a size ratio of 4:3.
The missing width is 90 cm.
FAQ
What does a size ratio mean?
A size ratio tells you how height compares to width. A ratio of 4:3 means the height has 4 parts for every 3 parts of width. The actual unit does not matter as long as both measurements are converted consistently.
Can height and width use different units?
Yes, physical length units can differ: for example, height in inches and width in centimeters. Pixel measurements must use pixels together. A pixel-to-physical conversion requires a specified pixel scale, so the calculator does not assume a DPI.
Why does the calculated ratio show as something like 1.7778:1?
When height and width are entered, the calculator divides height by width and reports the result against 1. For example, 16:9 becomes 1.7778:1 because 16 divided by 9 is approximately 1.7778.
