Line Efficiency: Five Ways Factories Get It Wrong
Line efficiency is the most quoted and most abused number on a sewing floor. The formula is short: earned minutes divided by attended minutes. The abuse hides in what gets counted on each side, and five particular mistakes recur so often they deserve names.
The formula, precisely
Earned minutes are pieces produced times the SMV of what was produced. Attended minutes are operators present times the minutes they were present. The line efficiency calculator does the division; the integrity of both inputs is where factories diverge.
The five mistakes
1. Earned against a soft SMV. If the SMV is typed rather than measured, efficiency inherits the error: a generous SMV manufactures phantom efficiency, a tight one slanders the line. The number is only as honest as the standard behind it.
2. Denominators that ignore attendance. Dividing by scheduled operators rather than present ones blames the line for people who were not there. Attended means attended: absences out, borrowed operators in, partial hours as partial hours.
3. Off-standard time vanished. Power cuts, waiting for feeding, machine down, no work: minutes the line attended but could not earn. Deleting them flatters the number and hides exactly the losses management should see; the honest treatment is to keep them in attended time and let the loss tree name them.
4. Mixed styles averaged into mush. A line that ran two styles at different SMVs earned each separately. Blending pieces at an average SMV produces a number that is precisely wrong; earned minutes must be computed per style and summed.
5. The daily number worshipped alone. A day's efficiency swings with changeovers and luck. The truthful signals are the trend over a window and the same-window comparison before and after any change, the equal-window discipline that separates improvement from anecdote.
Why the pedantry pays
Efficiency drives costing, planning, and pay in most factories. Compute it five different ways in five modules and every meeting becomes an argument about whose number is real; this is why the formula deserves exactly one implementation that every screen references. Compute it one honest way and the number turns into an instrument: when it moves, something on the floor actually happened, and the decomposition says what.