Enter the total inspiratory time and the total expiratory time into the I:E Ratio Calculator. The calculator will evaluate and display the I:E Ratio. 

I:E Ratio Calculator

Enter ventilator settings or breath times to calculate the I:E ratio.
RR + Ti
Target ratio
Direct times
breaths/min
seconds
breaths/min
E part
seconds
seconds

I:E Ratio Formula

The I:E ratio compares inspiratory time to expiratory time in one breath cycle.

RR + Ti mode

\begin{aligned}
T_{cycle} &= \frac{60}{RR}\\
T_e &= T_{cycle} - T_i\\
I:E &= T_i:T_e
\end{aligned}

Target ratio mode

\begin{aligned}
T_{cycle} &= \frac{60}{RR}\\
T_i &= \frac{T_{cycle}}{1 + E}\\
T_e &= T_{cycle} - T_i
\end{aligned}

Direct times mode

\begin{aligned}
T_{cycle} &= T_i + T_e\\
RR &= \frac{60}{T_{cycle}}\\
I:E &= T_i:T_e
\end{aligned}
  • RR = respiratory rate, in breaths per minute
  • Tcycle = total breath cycle time, in seconds
  • Ti = total inspiratory time, in seconds
  • Te = total expiratory time, in seconds
  • E = expiratory part of a target ratio written as 1:E

The displayed ratio is normalized. If expiration is longer, the result is shown as 1:E. If inspiration is longer, it is shown as an inverse ratio such as 2:1. In RR + Ti mode, inspiratory time must be less than the total cycle time.

Useful I:E Ratio Tables

Common I:E ratio ranges

I:E result Meaning Typical note
1:2 to 1:4 Expiration is 2 to 4 times inspiration Common passive ventilation range
1:1 to 1:1.5 Shorter expiratory time May need review for air trapping risk
1:5 or higher Long expiratory time Can occur with lower rates or short Ti
2:1, 3:1 Inspiration is longer than expiration Inverse ratio pattern

Cycle time by respiratory rate

Respiratory rate Cycle time Ti for 1:2 Ti for 1:3
10 breaths/min 6.00 s 2.00 s 1.50 s
12 breaths/min 5.00 s 1.67 s 1.25 s
15 breaths/min 4.00 s 1.33 s 1.00 s
20 breaths/min 3.00 s 1.00 s 0.75 s
30 breaths/min 2.00 s 0.67 s 0.50 s

I:E Ratio Notes

Use total inspiratory time for Ti. If a ventilator setting separates flow time and inspiratory pause, include the pause when you want the full mechanical I:E ratio.

Example: if RR is 20 and Ti is 0.8 seconds, cycle time is 3.0 seconds. Te is 2.2 seconds, so the I:E ratio is about 1:2.75.

I:E ratio is only one part of ventilator assessment. Interpret it with the full ventilator mode, waveform, patient condition, and local protocol.