Calculate inspiratory to expiratory ratio, inspiratory time, or expiratory time from two values and get decimal Ti/Te and I:E ratio.
Disclaimer: This calculator is for educational purposes only and is not medical advice. Do not use it to set or change ventilator settings or treatment—consult a qualified clinician for medical decisions.
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Inspiratory To Expiratory Ratio Formula
The inspiratory to expiratory ratio compares inspiratory time, Ti, with expiratory time, Te. This calculator uses the decimal form of the ratio, where:
IE = Ti / Te
To solve for inspiratory time:
Ti = IE * Te
To solve for expiratory time:
Te = Ti / IE
- IE = inspiratory to expiratory ratio as a decimal, equal to Ti/Te
- Ti = duration of inspiration
- Te = duration of expiration
The calculator converts entered time values to seconds before calculating. If you enter Ti and Te, it calculates the decimal IE ratio. If you enter Te and IE, it calculates Ti. If you enter Ti and IE, it calculates Te. The result is also shown as a colon ratio, such as 1:2 or 1:3.
Common I:E Ratio Conversions
Use this table to compare decimal IE values with common colon-style I:E ratios.
| Colon I:E ratio | Decimal IE value | Meaning |
|---|---|---|
| 1:1 | 1.0000 | Inspiration and expiration are equal |
| 1:2 | 0.5000 | Expiration lasts twice as long as inspiration |
| 1:3 | 0.3333 | Expiration lasts three times as long as inspiration |
| 2:1 | 2.0000 | Inspiration lasts twice as long as expiration |
Example Calculations
Example 1: Calculate the IE ratio
If the duration of inspiration is 1 second and the duration of expiration is 2 seconds:
IE = Ti / Te = 1 / 2 = 0.5
The decimal IE value is 0.5000, which corresponds to a colon ratio of 1:2.
Example 2: Calculate expiratory time
If the duration of inspiration is 0.8 seconds and the IE decimal value is 0.4:
Te = Ti / IE = 0.8 / 0.4 = 2
The duration of expiration is 2 seconds. The I:E ratio is 1:2.5.
FAQ
How do you convert a colon I:E ratio to a decimal?
Divide the inspiratory part by the expiratory part. For example, 1:2 becomes 1 ÷ 2 = 0.5. A 1:3 ratio becomes 1 ÷ 3 = 0.3333.
Why does the calculator use Ti/Te instead of a colon ratio?
The decimal form is easier to calculate with. Once the decimal is known, it can be converted back into the familiar colon format. For values below 1, the calculator displays the result as 1:x. For values above 1, it displays the result as x:1.
Should inspiration and expiration be entered in the same unit?
They do not have to be entered in the same unit because the calculator converts both values to seconds before calculating. However, respiratory timing is usually measured in seconds, so check your units if a duration is unusually large.
