Time Study Calculator

Observed time = mean of the timed cycles
Normal time = Observed time × Rating factor
Standard time = Normal time × (1 + Allowance)

• Rating factorobserver judgement of pace against a normal worker; 1.00 is normal, 1.10 is 10% faster than normal
• Allowanceadded fraction covering personal needs, fatigue, and unavoidable delay (PF&D)
• Normal timehow long the task takes at a normal pace, before any allowance
• Standard timethe figure used for costing, capacity planning, and line balancing

• Two allowance conventions are in circulation and they do not agree. This uses the percentage-of-normal-time form, Standard = Normal × (1 + A). The percentage-of-total-work-time form, Standard = Normal / (1 - A), gives 38.82 seconds on the same inputs, a 2.3% difference that compounds across a full line balance. State which one your standards were built on.
• Rating is the weakest link in the whole method and the one that gets challenged in a grievance. Trained analysts using the same video routinely differ by 5 to 10 percentage points, which is why rating practice against benchmark films is part of the qualification and why a lone unrated study is hard to defend.
• Five cycles is enough to demonstrate the arithmetic and not enough to set a standard. The required sample follows from the observed variability and the confidence and precision you want; the standard formula is n = (40 × sqrt(n′·Σx² minus (Σx)²) / Σx)² for 95% confidence and ±5% precision, and high-variability tasks can demand fifty cycles or more.
• Strip outliers only when you can name the cause. A cycle interrupted by a dropped part or a supervisor question is not part of the task and comes out with a written note; a slow cycle with no explanation stays in, because it is telling you the method is not stable.
• Allowances of 10% to 15% cover ordinary bench work. Heavy lifting, heat, awkward posture, or high visual concentration justify more, and the ILO tables assign specific increments per condition rather than leaving it to judgement.