TAHA Engineering Toolsby TAHA Knowledge Lab

Industrial & Manufacturing

Assembly Line Balancing Calculator

Cycle time, minimum workstations, line efficiency and balance delay for an assembly line.

Inputs

Calculate from
Bar chart of four workstations with loads 27, 28, 28 and 7 seconds under a dashed line at the 30 second required cycle time; the gaps above the bars are idle time.27 sS1tasks 1, 228 sS2tasks 3, 428 sS3tasks 5, 67 sS4tasks 7required cycle time C = 30 sidle
Each column is a workstation; its height is the station load (sum of its task times). No load may exceed the required cycle time C. The grey gap above each column is idle time per cycle. (Shows the worked example.) Diagram not to scale.

Shift time minus planned breaks.

Enter up to 10 tasks. “After” lists the tasks that must be finished first (leave empty if none). Leave unused rows empty.

Result

Line efficiency
75%
Required cycle time
30
Total work content
90
Theoretical minimum workstations
3stations
Workstations used
4stations
Total idle time per cycle
30
Balance delay
25%
Station loads
S1: 27 s (tasks 1, 2) S2: 28 s (tasks 3, 4) S3: 28 s (tasks 5, 6) S4: 7 s (task 7)
Stations over the cycle time
None

To make 900 units in 450 min, a unit must leave the line every 30 s. The work needs at least 3 stations; this balance uses 4 stations, giving 75% line efficiency and 30 s of idle time per cycle.

  • Tasks were assigned with the largest-candidate rule: a simple heuristic that respects the “after” order but does not guarantee the fewest possible stations.
  • The theoretical minimum is a lower limit; precedence and task sizes often make it impossible to reach.

Educational estimate — check the assumptions below.

About this calculator

Line balancing divides the tasks of an assembly job between workstations so that each station has about the same amount of work, and none has more than the time available per unit (the cycle time set by required output). A well-balanced line needs fewer stations and wastes less idle time. Enter your tasks, their times and which tasks must be done first. You can let the calculator assign stations with a standard heuristic, or enter your own assignment and check it.

Formula

Assign tasks for me

Required cycle time C = Available time ÷ Required output

Minimum stations = ⌈ Σt ÷ C ⌉    Efficiency = Σt ÷ (N × C)

Idle time = N × C − Σt    Balance delay = 1 − Efficiency

Σt = total work content (sum of task times), N = stations used, ⌈ ⌉ = round up. Largest-candidate rule: open a station; repeatedly add the longest task whose predecessors are already assigned and which still fits in the remaining time; when nothing fits, open the next station.

I assign the stations

Same formulas, using your station numbers. Each station load (sum of its task times) is compared with the cycle time, and every task’s predecessors must be in the same or an earlier station.

Worked example

Available time 450 min per shift, required output 900 units. Seven tasks (seconds): 1 = 12; 2 = 15 after 1; 3 = 8 after 1; 4 = 20 after 2; 5 = 10 after 3; 6 = 18 after 4 and 5; 7 = 7 after 6.

  • Cycle time = 27 000 s ÷ 900 = 30 s
  • Work content = 12 + 15 + 8 + 20 + 10 + 18 + 7 = 90 s → minimum stations = ⌈90 ÷ 30⌉ = 3
  • Largest-candidate rule: S1 = tasks 1, 2 (27 s) · S2 = tasks 3, 4 (28 s) · S3 = tasks 5, 6 (28 s) · S4 = task 7 (7 s) → 4 stations
  • Efficiency = 90 ÷ (4 × 30) = 75%; idle time = 120 − 90 = 30 s; balance delay = 25%

Three stations would need loads of exactly 30 s each, which the task sizes and order do not allow — so here the theoretical minimum cannot be reached.

Assumptions and limitations

  • One product, one worker per station, and task times that are fixed averages (no variation).
  • Automatic assignment uses the largest-candidate rule, a well-known heuristic. It respects task order but does not search every possible assignment, so a better balance may exist.
  • Tasks longer than the cycle time cannot fit in any single station; in automatic mode they are rejected with an explanation.
  • Zoning limits (tasks that must or must not share a station), walking time and learning effects are not included.

References

  • Groover, Automation, Production Systems, and Computer-Integrated Manufacturing — line balancing and the largest-candidate rule.