What is a cycle time study?
A cycle time study (or stopwatch time study) measures how long each part of an operation really takes. Observing several cycles shows not just the average but the variation, which is often the bigger problem: an element that usually takes 18 seconds but sometimes 26 will disrupt flow. The results feed standard work, line balancing, capacity planning and costing.
Time study calculations
| Step | Formula |
|---|---|
| Observed time per element | Mean of the valid readings |
| Normal time | Observed time × performance rating |
| Standard time | Σ normal times × (1 + PF&D allowance) |
| Readings needed (±5%, 95%) | n′ = (40 × √(nΣx² − (Σx)²) ÷ Σx)² |
| Unusual readings | Outside Q1 − 1.5 IQR or Q3 + 1.5 IQR of the element's readings |
Time study example
An industrial engineer times six elements of a controller assembly over ten cycles. One reading of the screw-driving element, 25.6 seconds against a typical 18, is flagged: the operator dropped a screw. Excluding it, the average observed cycle is about 55.5 seconds. With ratings (the screw-driving operator worked at 105%, the cable connection at 95%) and a 12% allowance, the standard time is about 62.7 seconds, above the 60-second takt. The station needs rebalancing or a faster screw-driving method before it can meet demand.
Tips for better time studies
- Explain why you are there. Time studies are about the process, not the person. Involve the operator.
- Define break points that can be seen or heard (part placed, tool released) so every reading starts and stops at the same point.
- Separate manual and machine time. Machine elements barely vary; manual ones do.
- Note every interruption rather than silently discarding it: abnormal readings show real problems.
- Study the standard method, or you will time a method that should be changed first. Look for waste.
How to use this Cycle Time Analysis tool
- Define the elements. List the work elements of the operation in order, each with a clear start and end point.
- Record the observations. Choose the number of cycles and type or paste the observed seconds for each element (copy straight from Excel).
- Rate and set allowances. Enter a performance rating for each element and the PF&D allowance for the job.
- Review unusual readings. Readings outside the normal spread are flagged; exclude them from the means if they were interruptions.
- Check the sample size. The tool shows how many readings each element needs for ±5% precision at 95% confidence.
- Get the standard time. Read the normal and standard times, compare them with takt and export the time study to PDF or Excel.
Frequently asked questions
What is cycle time?
Cycle time is how long a process step takes to complete one unit, from the start of one unit to the start of the next. It is measured at the process, usually with a stopwatch time study or from machine data, and compared with takt time, the pace customers require.
How do you do a time study?
Break the operation into work elements with clear start and end points, observe and time each element over several cycles, rate the operator's pace, then calculate the normal time (mean × rating) and add allowances for personal needs, fatigue and delays to get the standard time.
How many cycles should I observe?
Enough to estimate the mean precisely. This tool uses the common formula n′ = (40√(nΣx² − (Σx)²) ÷ Σx)², which gives the number of readings for ±5% precision at 95% confidence. Elements with high variation need more readings; 10 to 20 cycles is typical for short manual work.
What is a performance rating?
A rating adjusts observed times to a normal pace. 100% is normal; an operator working faster than normal is rated above 100% (e.g. 110%), slower below. Rating needs training and is often the least reliable part of a time study, so many companies use pre-determined time systems like MTM for comparison.
What are PF&D allowances?
Personal, fatigue and delay (PF&D) allowances add time for personal needs, recovery from fatigue and unavoidable minor delays. They are expressed as a percentage of normal time, typically 10% to 20% depending on the physical demands and environment.
What is the difference between cycle time, lead time and takt time?
Cycle time is how often a step completes a unit. Lead time is how long one unit takes to travel through the whole process, including waiting. Takt time is the rate the customer requires. Reducing waiting cuts lead time; balancing work cuts cycle time to meet takt.