Why Measure Work?
You cannot balance a line, set a production rate, cost a product, or identify waste without accurate time data. Time study is the industrial engineer's most fundamental skill — and the most commonly done poorly.
Bad time data cascades everywhere: inaccurate cost estimates, unrealistic production schedules, unbalanced lines, and standards that operators either cannot meet or easily exceed. Getting the measurement right is worth the effort.
Three Methods of Work Measurement
1. Stopwatch Time Study
The most common method. An observer times an operator performing a task for multiple cycles, applies a performance rating, and adds allowances to calculate the standard time.
The Standard Time Formula
Standard Time = (Average Observed Time) × (Performance Rating) × (1 + Allowance %)
Example: Observed average = 45 seconds, rating = 1.05 (slightly faster than normal), allowance = 15%. Standard Time = 45 × 1.05 × 1.15 = 54.3 seconds
2. Predetermined Time Systems (PTS)
Instead of timing actual work, PTS breaks tasks into fundamental motions (reach, grasp, move, position, release) and assigns time values from published tables. The two most common systems:
| System | Granularity | Best For |
|---|---|---|
| MTM (Methods-Time Measurement) | Very detailed — individual finger/hand motions | Highly repetitive, short-cycle assembly tasks |
| MOST (Maynard Operation Sequence Technique) | Activity-level sequences (general move, controlled move, tool use) | Faster to apply, good for medium-cycle tasks, widely used in industry |
PTS advantages: no performance rating needed (times are pre-normalized), can set standards before the process even exists (for new product launches), and eliminates observer bias.
3. Work Sampling
Instead of continuously timing one operator, randomly observe many operators throughout the day and record what they are doing at each observation (working, waiting, walking, etc.). Useful for understanding how time is spent across a department and identifying the proportion of value-added vs. non-value-added activity.
Common Allowances
| Category | Typical % | What It Covers |
|---|---|---|
| Personal | 5% | Bathroom, water, stretching |
| Basic Fatigue | 4% | Normal physical tiredness over a shift |
| Variable Fatigue | 0-15% | Heavy lifting, awkward posture, heat, noise (see ergonomics) |
| Unavoidable Delays | 2-5% | Tool changes, receiving instructions, minor machine adjustments |
Using Time Study Data
| Application | How Time Data Is Used | Related Guide |
|---|---|---|
| Line Balancing | Assign work elements to stations based on element times vs. takt | Line Balancing |
| Standard Work | Define the expected cycle time and work sequence for each station | Standard Work |
| Capacity Planning | Calculate demonstrated capacity from standard times and OEE | Capacity Planning |
| Product Costing | Labor cost per unit = standard time × labor rate | — |
| SMED | Time each changeover element to separate internal from external | SMED |
| Incentive Systems | Set fair performance targets based on measured standards | — |
✅ Good Time Study Practice
- 10+ cycles observed minimum
- Elements clearly defined with breakpoints
- Operator informed and comfortable being timed
- Performance rating applied honestly
- Allowances appropriate for actual conditions
- Data used to improve process, not punish people
❌ Time Study Mistakes
- Timing 2-3 cycles and calling it a standard
- Timing the fastest operator as the baseline
- No performance rating applied
- Forgetting allowances (setting unreachable standards)
- Using time study as a surveillance tool
- Never updating standards when the process changes
Time Study Is Not Surveillance
The purpose of time study is to understand and improve the process — not to monitor or punish people. Always explain to operators why you are timing, how the data will be used, and that the goal is to make the work better (eliminate waste, improve ergonomics, balance workload), not harder. Build trust by sharing the results and acting on what you find.
🎯 Key Takeaway
Accurate time data is the foundation of almost everything an IE does: balancing lines, setting standard work, planning capacity, and costing products. Invest in doing it right — enough cycles, proper rating, appropriate allowances — and the downstream decisions will be sound. Cut corners on measurement, and every decision built on that data will be wrong.
Interactive Demo
Run a stopwatch time study. Observe 10 cycles, apply rating factors, and calculate the standard time.
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