How to Calculate SMV: Time Study Method with Example

This guide shows how to calculate SMV from time study on the factory floor. It is the method most factories use to check predetermined SMVs, set standards for new operations, and verify improvements.

The formula#

• $t_{obs}$ is the average observed cycle time in seconds
• $R$ is the performance rating in percent (100 = standard pace)
• $A$ is the allowance in percent

The first two terms give the basic time in minutes. The allowance turns basic time into standard time.

Step 1: Define the operation and method#

Write down exactly where the operation starts and ends, for example "pick up two front panels from bundle, align shoulders, sew both shoulders with overlock, trim chain, place aside". If the start and end points are not fixed, different observers will time different things.

Check that the method is the one you want to standardise: correct machine, attachment, stitch density and workplace layout. There is no point setting a standard for a poor method.

Step 2: Choose the operator#

Time a trained operator who has been on the operation long enough to work consistently. Avoid learners and the single fastest person on the line. Tell the operator what you are doing and why.

Step 3: Time the cycles#

Record at least 10 cycles for short operations (under about 30 seconds) and at least 5 for long ones. More cycles give a steadier average. Continuous timing on video is easiest to review later.

Step 4: Remove abnormal cycles#

Cycle 5 (38.2 s) included a thread break. Thread breaks, bobbin changes and interruptions are not part of the normal cycle; remove them from the average and cover them with the allowance (or measure them separately if they are frequent and regular).

Average of the nine normal cycles:

(24.1 + 23.8 + 25.0 + 24.6 + 23.9 + 24.4 + 24.8 + 24.2 + 25.1) / 9 = 219.9 / 9 = 24.43 s

Step 5: Rate the performance#

Judge the operator's pace against standard pace. A rating of 100% is standard; 110% means the operator worked 10% faster than standard; 90% means slower. Rating is a skill: engineers train on rating films and cross-check each other.

For this example, the operator is rated at 105%.

Basic time = 24.43 / 60 × 1.05 = 0.4275 min

Step 6: Add allowances#

Allowances cover personal needs, fatigue and small delays that belong to normal work. The percentage is a company policy, often between about 10% and 20% for sewing work, and sometimes different for machine and manual elements. Use your factory's policy.

With a 15% allowance:

SMV = 0.4275 × 1.15 = 0.492 min

Step 7: Check the result#

• Compare with the predetermined SMV if you have one. A large gap means a method difference or a rating problem.
• Check that the SMV gives a sensible hourly capacity: 60 / 0.492 = 122 pieces per hour at 100%.
• Time a second operator if the operation is important or the result looks odd.

From operations to the garment#

Repeat for every operation and add them up. The garment SMV calculator takes observed times and ratings for each operation and builds the total.

Common mistakes#

• Averaging abnormal cycles into the observed time. One thread break in ten cycles can add several percent.
• No rating. Unrated time study copies the operator's speed into the standard.
• Changing the start and end points between cycles.
• Timing during the first days of a style. Operators are still learning; the times are too long.
• Applying the allowance twice, once in the observed time (by leaving interruptions in) and again as a percentage.

When to redo the SMV#

Recalculate when the method, machine, attachment, fabric or specification changes, or when efficiency on the operation is consistently far above or below 100% after the learning period. SMVs are living numbers.

Related reading: what SMV means, time study and line balancing.

Related guides#

• SAM vs SMV: the difference between SAM and SMV.
• CM cost: turning SMV into the cost of making.