File Compression Ratio Calculator
Compare original and compressed file sizes to show ratio and percentage size change.
How to use this calculator
- Enter both positive sizes using the same unit.
- Confirm that all inputs use the stated units and the same population, period or scope.
- Change one assumption at a time when comparing scenarios.
Formula used by the file compression ratio calculator
Ratio = original ÷ compressed; reduction% = (original − compressed) ÷ original × 100
- Ratio = original ÷ compressed; reduction% = (original − compressed) ÷ original × 100
- Some compression methods or file types can increase size; negative reduction is valid and should not be hidden.
- Inputs are validated against required ranges and outputs are rounded for readability.
Worked examples
Worked example
A 250 MB file becomes 75 MB.
The ratio is 3.33:1 and the size reduction is 70%.
The ratio is 3.33:1 and the size reduction is 70%.
Understanding the result
Compare original and compressed file sizes to show ratio and percentage size change.
Some compression methods or file types can increase size; negative reduction is valid and should not be hidden.
Important notes
Some compression methods or file types can increase size; negative reduction is valid and should not be hidden.
Use the result as a calculation aid for the inputs supplied; confirm critical specifications independently.
Frequently asked questions
What does 3:1 mean?
The original file is three times the size of the compressed file.
Can compression increase size?
Yes; then the size reduction is negative.
How do I use this calculator?
Enter both positive sizes using the same unit.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- How to Calculate Percentage Change — Learn the percentage change formula, how to calculate increases and decreases, and why the original value matters.
- Percentage Change vs Percentage Difference — Understand the difference between percentage change and percentage difference, including when each formula is appropriate.
- Percentage Change — Learn what percentage change means, how to calculate increases and decreases, and how the original value affects the result.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.