Lean Manufacturing

Time Study and Standard Time: Building Accurate Labor Routings

Labor routings only help planning and costing when the standard time reflects the job as it is really run. This guide shows how time study data turns observed work into a routing that people can trust.

Time study is the systematic observation and measurement of work elements to establish a standard time for a defined operation performed at a defined method. The MAYNARD process for a valid time study has six steps: document the method (workstation layout, tools, part orientation), define work elements (discrete measurable units of work with definite start and stop points), observe and time a statistically sufficient number of cycles (typically 10 to 30 depending on cycle length and variability), apply a performance rating factor to each observed time to normalize to 100% pace, average the normalized times to get normal time, and add allowances for personal needs, fatigue, and unavoidable delays to get standard time. Standard time = normal time x (1 + allowance percentage), where allowance is typically 10% to 15% for most manual assembly operations.

Performance rating is the step most likely to introduce error into a time study because it requires the observer to judge whether the operator is working at normal, fast, or slow pace. A 0.85 rating applied to a 0.45-minute observed cycle gives a 0.38-minute normal time. A 1.15 rating on the same cycle gives a 0.52-minute normal time. The 0.14-minute difference is a 37% variation from the same observation, which is why inter-rater reliability is critical. MOST (Maynard Operation Sequence Technique) and MTM-2 (Methods-Time Measurement) are predetermined time systems that eliminate rating by breaking work into standard motion categories with assigned times, producing consistent results regardless of who performs the study. For high-volume operations where labor standard accuracy is critical, predetermined time systems typically produce more defensible results than stopwatch time study.

Allowance percentage is the often-underdiscussed component that affects standard time significantly. Personal allowance of 5% (approximately 24 minutes in an 8-hour shift) is standard for most operations. Fatigue allowance ranges from 4% for light, non-repetitive work to 12% or more for heavy or highly repetitive work. Machine delay allowance accounts for unavoidable machine interference, quality checks, and minor adjustments that are part of the method but cannot be reduced by operator pace. Total allowances of 12% to 18% are typical for assembly operations. If a time study team uses 10% allowance when 15% is appropriate, standard time is understated by 5 percentage points, and operators will systematically miss the standard not because of poor performance but because the standard is wrong.

Standard time routing must be updated when methods change, not just when complaints arrive. A 2018 standard time for a product modified 3 times since then is not a valid standard for the current method. Common triggers for standard time re-study are: new tooling or equipment at a station, work content changes from engineering change orders, product mix shifts that change average station loading, new operator training standard established for the operation, and ergonomic improvements that change the method. Plants should have a policy defining which triggers require a formal re-study versus an estimate adjustment, and a register tracking study dates so standards older than 5 years on changed products are flagged for review.

Connect standard time routings to scheduling and capacity planning to realize their full value. A time standard that lives only in the labor routing record and is never used to set daily output targets, load work centers, or staff shifts has limited operational impact. The standard becomes a planning tool when supervisors are assigned a daily output target calculated as available hours multiplied by parts per hour (1 / standard time), when scheduling loads work centers based on standard hours of work per period, and when actual hours versus standard hours is reviewed daily to identify where the process is losing time. Standard time routing combined with actual performance tracking creates the feedback loop that makes improvement work measurable and sustains it past the initial kaizen event.

Published 2026-05-28.