OpenSpecEngineering

Turns a stopwatch time study into a standard time: the time a qualified operator, working at a normal pace, needs to make one unit, with allowances for rest and delays. It also gives the output rate per hour and per 8-hour shift. Industrial engineers, supervisors and estimators use it to set labor standards, plan staffing and price jobs [1], [2].

Equations

NT = OT · (R / 100) / n     ST = NT · (1 + A / 100)

OT is the observed (selected) time for one cycle, usually the mean of the timed readings for that element. R is the performance rating in percent: 100 is the normal pace, 110 means the operator worked 10 % faster than normal. n is the number of units one cycle makes. NT is the normal time per unit. A is the allowance for personal needs, fatigue and unavoidable delay (PF&D), in percent. ST is the standard time per unit.

Some plants state the allowance as a share of the whole workday instead of a share of normal time [1]. Then the operator works only (100 − A) % of the day, and

ST = NT / (1 − A / 100)

The page shows both. The output rate is 60/ST units per hour, and 480/ST units per 480-minute shift.

Limits and common mistakes

• Use the same allowance basis as the rest of your plant’s standards. The two bases differ more as A grows: at 15 % they differ by about 2 %, at 30 % by about 10 %.
• The observed time must be for one cycle. If a cycle makes several units, enter the count in Units Produced per Cycle, not a time already divided by it.
• The shift output assumes 480 working minutes. A shift with paid breaks already covered by the allowance should not have them taken out again.
• Whether you have timed enough cycles is a separate question; see the Time Study Sample Size calculator.

Worked example

An analyst times an assembly operation over 20 cycles. The mean is 0.80 min per cycle, one unit per cycle, and she rates the operator at 110 %. The plant uses a 15 % PF&D allowance. What is the standard, and how many units should a shift make?

1. Enter Observed (Selected) Time per Cycle 0.80 min and Performance Rating 110.
2. Enter Allowances — PF&D 15 and Units Produced per Cycle 1.
3. Press Solve. The Solution shows: Normal time per unit: 0.88 min
   Standard time per unit (allowance on normal time): 1.012 min
   Standard time per unit (allowance as fraction of workday): 1.03529 min
   Standard output rate: 59.2885 units/hr
   Standard output per 8-hour shift: 474.308 units

Check by hand. 0.80 × 1.10 = 0.88 min, and 0.88 × 1.15 = 1.012 min. 480 / 1.012 ≈ 474 units. On the workday basis, 0.88 / 0.85 = 1.035 min, about 2 % longer, as expected for a 15 % allowance.