Availability is the first of the three OEE factors, and the one that usually loses the most time on a CNC floor. The formula fits on one line; the work is in counting run time honestly.
The availability formula
Availability = Run time ÷ Planned production time × 100
- Planned production time = shift length minus planned breaks.
- Run time = planned production time minus all stops — breakdowns, setups, waiting for material or an operator.
A second, reliability-engineering version uses failure history instead of a shift log: Availability = MTBF ÷ (MTBF + MTTR). Both are worked out side by side in the availability calculator.
A worked example
One 8-hour shift on one machine (illustrative numbers):
Shift length
- Minutes
- 480
Planned breaks
- Minutes
- 30
Planned production time
- Minutes
- 450
Stops (setup 35, waiting for material 18, alarm 10)
- Minutes
- 63
Run time
- Minutes
- 387
| Input | Minutes |
|---|---|
| Shift length | 480 |
| Planned breaks | 30 |
| Planned production time | 450 |
| Stops (setup 35, waiting for material 18, alarm 10) | 63 |
| Run time | 387 |
Availability = 387 ÷ 450 = 86%. Notice that the setup alone cost more than the alarm and the material wait together — the formula only gives the percentage, so the stops behind it need to be logged by reason to be useful. Multiply it by performance and quality to get OEE — try that in the OEE calculator.
Availability vs uptime vs utilization
Uptime
- Divides
- time not broken down ÷ total time
- Answers
- Could the machine run?
Availability
- Divides
- run time ÷ planned production time
- Answers
- Did it run when planned?
Utilization
- Divides
- run time ÷ total available time
- Answers
- How much of all its time did it run?
| Measure | Divides | Answers |
|---|---|---|
| Uptime | time not broken down ÷ total time | Could the machine run? |
| Availability | run time ÷ planned production time | Did it run when planned? |
| Utilization | run time ÷ total available time | How much of all its time did it run? |
Availability only judges the hours you scheduled. To see the hours you didn’t schedule, use the machine utilization formula instead.