Time Study

What Is a Time Study?

A time study is a quantitative method of measuring work. An analyst observes a qualified worker performing a defined task, records the time taken for each element, applies a performance rating to adjust for pace, and adds allowances for rest and unavoidable delays. The result is a standard time: the amount of time a trained worker, working at a normal pace, should require to complete that task.

Standard times feed directly into production planning, staffing decisions, cost estimating, and performance benchmarking. Without them, labour standards are guesswork, and improvement efforts have no reliable baseline to measure against.

Origins: Frederick Winslow Taylor and Scientific Management

Time study was systematised by Frederick Winslow Taylor in the 1880s at the Midvale Steel Company. Taylor believed that most industrial work was performed far below its potential efficiency, and that the solution was to break jobs into discrete elements, time each element, and establish scientifically derived standards. His 1911 book The Principles of Scientific Management made time study the foundation of industrial engineering.

Frank and Lillian Gilbreth later refined the approach by introducing motion study, analysing the physical movements within each timed element to eliminate wasted motion. Together, time and motion study became the backbone of what would eventually evolve into lean manufacturing.

The Standard Time Formula

The fundamental calculation in any time study is:

Standard Time = Observed Time x Performance Rating x (1 + Allowance Factor)

Each variable has a precise meaning:

• Observed Time (OT): The average actual time recorded across multiple cycles of the task.
• Performance Rating (PR): The analyst's assessment of the worker's pace relative to a defined "normal" rate. A worker performing at normal pace receives a rating of 1.0. Slower work is rated below 1.0; faster work above 1.0.
• Normal Time (NT): OT x PR. This is the time the task would take at exactly normal pace.
• Allowance Factor (AF): A percentage added to cover personal time (toilet breaks, drinking water), fatigue recovery, and unavoidable delays (machine setup waits, material shortages). Typical industrial allowances range from 10% to 20%.

Worked Numerical Example

A maintenance technician is observed replacing a conveyor belt tensioner. The analyst records 10 cycles and calculates an average observed time of 4.5 minutes per cycle. The worker is judged to be operating at 90% of normal pace (performance rating: 0.90). The plant standard allowance for maintenance tasks is 15%.

• Normal Time = 4.5 x 0.90 = 4.05 minutes
• Standard Time = 4.05 x (1 + 0.15) = 4.66 minutes

This standard time is then used to populate the relevant work order, set a realistic PM schedule duration, and calculate crew requirements for a planned shutdown.

Step-by-Step Time Study Process

A valid time study follows a defined sequence. Skipping steps introduces bias and invalidates the standard.

Step 1: Select the Task

Choose a task that is stable, repetitive enough to observe multiple cycles, and significant enough to justify the effort. Prioritise tasks that drive labour cost, affect throughput, or feed into maintenance planning schedules.

Step 2: Define and Break Down Task Elements

Divide the task into discrete, measurable elements with clear start and end points. Good elements are short (typically 0.04 to 0.30 minutes), homogeneous, and easy to observe. Separate machine-paced elements from operator-paced elements, and separate regular elements from irregular ones (e.g., tool retrieval that happens once every five cycles).

Step 3: Select a Qualified Worker

Observe a worker who is fully trained, experienced, and working at a representative pace. Studying a novice produces a time that is too long; studying the fastest worker produces a time that is too short. The worker should know they are being timed and why, which requires clear communication and, in unionised environments, agreement with labour representatives.

Step 4: Observe, Time, and Record

Use a stopwatch, time-study board, or electronic data collector to record the time at the end of each element. The two main timing methods are:

• Continuous timing: The stopwatch runs throughout; the analyst reads and records the cumulative time at each element break-point, then subtracts to find element times. More accurate for short elements.
• Snap-back (repetitive) timing: The stopwatch is reset to zero at each element break. Easier to read but loses time during the reset action, which must be accounted for.

Record a minimum of 10 to 30 cycles depending on task variability. More variable tasks require larger samples for statistical reliability.

Step 5: Apply the Performance Rating

Rate the worker's pace against a defined standard. The most common systems are the Westinghouse system (rating skill, effort, conditions, and consistency separately) and the British Standard Rating (pace rated on a 0 to 100 scale where 100 is "standard" and 133 is "maximum"). Organisations must choose one system and apply it consistently.

Step 6: Calculate Normal Time and Add Allowances

Multiply observed time by the performance rating to get normal time. Then determine the appropriate allowance factor from the company's standard allowance table or from a separate allowance study. Apply the formula to calculate standard time.

Step 7: Validate and Document

Cross-check the standard time against historical data and comparable tasks. Document the method, conditions, sample size, rating rationale, and allowance basis. A time study without documentation cannot be defended, revised, or audited later.

Types of Time Study Methods

Stopwatch time study is the most precise method for repetitive, short-cycle tasks. But it is not the only approach. The right method depends on task characteristics, cycle length, and resource availability.

Stopwatch Time Study

Direct observation with a stopwatch or electronic timer. Best for manual, repetitive tasks with cycle times between one and thirty minutes. High accuracy, but labour-intensive and subject to observer influence on worker behaviour.

Work Sampling

The analyst makes a large number of random, brief observations over an extended period and records what the worker or machine is doing at each instant. The proportion of observations in each category estimates the proportion of total time spent on each activity. Best for long-cycle, irregular, or non-repetitive tasks where continuous observation is impractical, such as maintenance rounds or supervisory work. Also used to measure idle time across a workforce.

Predetermined Motion Time Systems (PMTS)

PMTS methods (such as Methods-Time Measurement, or MTM, and MOST) establish standard times by decomposing a task into basic human motions (reach, grasp, move, position, release) and assigning a pre-validated time value to each motion from published tables. No direct observation is required once the task is defined. Highly consistent and objective, but requires trained specialists and is most accurate for assembly and short-cycle manufacturing tasks.

Computerised Time Study

Electronic data collectors, tablet applications, and video analysis software automate data capture and calculation. Video-based tools allow the analyst to review footage frame by frame, eliminating real-time observer pressure on the worker. Modern systems can export directly into CMMS or ERP platforms, reducing manual transcription errors.

Time Study vs Work Sampling vs MOST: Comparison

Time Study in Maintenance Operations

Time study is not limited to production lines. Maintenance teams use it to solve three persistent problems: not knowing how long jobs actually take, not knowing how much of a technician's day is productive, and not being able to justify staffing requests with data.

Measuring Wrench Time

Wrench time is the proportion of a maintenance technician's shift spent doing hands-on repair or maintenance work, as opposed to travelling, waiting for parts, looking for tools, or in planning meetings. Industry benchmarks place typical wrench time at 25% to 35% for reactive maintenance environments, rising to 45% to 55% in well-planned operations.

Work sampling is the standard method for measuring wrench time. Analysts conduct hundreds of random observations across a maintenance workforce over several weeks. The resulting data identifies where time is being lost and quantifies the opportunity for improvement before any investment is made.

Setting PM Task Durations

Preventive maintenance schedules require realistic time estimates per task. If a PM task is allocated 30 minutes but consistently takes 50 minutes, the planner will schedule too many jobs per shift, technicians will cut corners, and compliance rates will fall. Stopwatch time studies on representative PM tasks produce standard times that make schedules credible. These feed directly into maintenance planning and work order templates.

Crew Sizing

Standard times from time studies allow planners to calculate the total labour hours required to maintain an asset base or complete a shutdown. Dividing total required hours by available hours per technician per period gives the minimum crew size needed to keep up with planned work without building an unmanageable backlog.

Benchmarking Against Cycle Time and Takt Time

In integrated manufacturing environments, maintenance standard times are compared against cycle time and takt time to determine whether maintenance windows fit within production rhythms. If a bearing replacement takes longer than the available maintenance window between production cycles, the task must be redesigned, a spare must be staged, or the schedule must be restructured.

Impact on Overall Equipment Effectiveness

Accurate standard times for maintenance tasks improve Overall Equipment Effectiveness (OEE) planning. When planned maintenance durations are realistic, planned downtime is shorter and more predictable, reducing the gap between planned and actual availability. They also provide the basis for evaluating whether investing in faster repair methods or better tooling yields a measurable return.

Time Study and Standard Operating Procedures

A time study and a Standard Operating Procedure (SOP) are complementary documents. The SOP defines how a task must be performed; the time study measures how long it takes when performed correctly. A standard time derived from a study where the worker was not following the SOP is invalid. For this reason, time studies should always be conducted after the method is standardised and the SOP is established, not before.

Common Mistakes and How to Avoid Them

Frequently Asked Questions

The Bottom Line

A time study translates direct observation into a defensible, repeatable standard time that teams can use to plan work, size crews, and measure improvement. The formula is straightforward: Observed Time x Performance Rating x (1 + Allowance Factor). The discipline lies in the details: selecting the right worker, defining clean element boundaries, rating consistently, choosing appropriate allowances, and documenting everything.

For maintenance operations, time studies and work sampling are among the most underused tools available. They provide the factual foundation for showing where wrench time is going, why PM schedules slip, and how many technicians a facility actually needs. Without this data, every staffing decision and scheduling assumption rests on habit rather than evidence.

Used alongside standard operating procedures, production KPIs like cycle time and takt time, and OEE tracking, time studies give industrial and maintenance engineers a common language for quantifying work and driving genuine efficiency gains.