GFT instruments / Line-balancing studio
The illustrative T-shirt route needs eight stations for 300 garments in 420 net minutes. Start with six operators, edit the work, and see what constrains the line.
01 / The bench
No sourced programme SMVs were supplied. These teaching inputs are not a factory benchmark. Every result is derived from the inputs below, and the loom in the opening follows them.
Candidate staffing
operators required
2 additional operators for this assignment
This heuristic uses 8 stations, 2 more operators than the 6 entered. The aggregate lower bound is 7; precedence and task sizes explain why a workable assignment can need more. Station 5 sets the 1.35 min bottleneck cycle. Validate machines, skills and handling before moving work.
Yamazumi / workload by station
Work Idle at takt Overload
Editing: S5 · 07 Close side seams (1.35 min bottleneck against 1.40 min takt). Hover any block to inspect.
02 / Operation bulletin
EditingS5 · 07 Close side seams (1.35 min)
SMV means standard minutes per garment. Predecessors are comma-separated IDs that must be completed first. IDs stay fixed. Remove dependent links before removing an operation. The supported editor limit is 32 operations. Each thread is drawn to its SMV against the takt mark.
Live read-out · active focus
Editing: S5 · 07 Close side seams1.35 min on station S5 (bottleneck cycle 1.35 min against 1.40 min takt). 12 operations, 8.65 min total work.
03 / Method: keep the denominator visible
Illustrative route; blocks keep their operation colours. Do not combine observed seconds for one task with unadjusted standard minutes for another.
01 / Denominator
The shift boundary is net available production time for the whole line. Enter demand for that same period. SMV is the standard work content of an operation, in minutes per garment. Keep one allowance convention across the bulletin.
W = sum of SMVs = 8.65 min
02 / Takt
Divide net production minutes by the garments due in that window. Every station must finish inside this time, or the target slips. The ribbon is cut at each takt: the cuts count how many takts of work one garment holds.
t = 420 ÷ 300 = 1.40 min
03 / Ceiling
Round the work up to whole takts and you have the fewest stations arithmetic allows. It is a ceiling, nothing more: it ignores predecessors and task sizes, so a workable assignment can need more people.
Nmin = ceiling(8.65 ÷ 1.40) = 7
04 / Assignment
Tasks are sorted by descending SMV. Each station takes the largest unassigned task that fits the remaining takt and whose predecessors are placed. When nothing fits, a new station opens. It is a reproducible heuristic; it does not prove the smallest station count.
Stations = 8
05 / Efficiency
Balance efficiency divides the work by stations times the bottleneck cycle, so it describes how work is spread, not whether the target is achievable. Idle sums gaps below takt; overload sums excess above it. A task above takt gets a diagnostic station and no staffing answer.
E = 8.65 ÷ (8 × 1.35) = 80.1%
04 / Assignment and idle-time ledger
Minutes are per garment. Woven blocks run to each station's load; the hatched warp runs on to the dashed takt mark. A bullet identifies a bottleneck. An overloaded station means the target cannot be met under the indivisible-task assumption.
| Station | Operations in execution order | Cloth against takt | Load (min) | Idle (min) | Overload (min) |
|---|---|---|---|---|---|
| S1 | 01 Join shoulders 05 Hem sleeves | 1.25 | 0.15 | 0.00 | |
| S2 | 02 Prepare neck rib 03 Attach neck rib | 1.30 | 0.10 | 0.00 | |
| S3 | 04 Topstitch neck | 0.55 | 0.85 | 0.00 | |
| S4 | 06 Attach sleeves | 1.15 | 0.25 | 0.00 | |
| S5 • | 07 Close side seams | 1.35 | 0.05 | 0.00 | |
| S6 | 08 Hem body 09 Attach label | 1.30 | 0.10 | 0.00 | |
| S7 | 10 Trim threads 11 Inspect | 1.25 | 0.15 | 0.00 | |
| S8 | 12 Fold | 0.50 | 0.90 | 0.00 |
Reconciliation: work + idle at takt = stations × takt + overload, even when the target is infeasible8.65 work + 2.55 idle = 8 stations × 1.40 takt + 0.00 overload
05 / A and B, one scale
A is the illustrative default, saved for you, drawn as an outline. B is the current inputs, woven. Drag the divider to wipe between them. The saved inputs remain fixed in this tab, the share link contains B, and calculations run locally in the browser.
A illustrative default, pre-saved: 8 stations, takt 1.40 minB current inputs: 8 stations, takt 1.40 min
| Decision measure | Saved A | Current B |
|---|---|---|
| Target garments | 300 | 300 |
| Net minutes | 420 | 420 |
| Available operators | 6 | 6 |
| Routing | precedence | precedence |
| Total work (min) | 8.65 | 8.65 |
| Takt (min) | 1.40 | 1.40 |
| Feasible at target | Yes | Yes |
| Heuristic stations | 8 | 8 |
| Additional operators | 2 | 2 |
| Bottleneck cycle (min) | 1.35 | 1.35 |
| Balance efficiency | 80.1% | 80.1% |
06 / Interlude: follow the loss beyond the balance
11.20 station-minutes per garment: 8.65 woven, 2.55 hanging as slack, 0.00 overload. Availability, performance and quality losses are not modelled here.
Idle at takt -2.55 min Gap below the takt guide: the slack loops, one per station with idle time.
Use the OEE instrument ↗ to separate availability, performance and quality within a shift. Labour cost and ramp planning are related decisions; this studio does not calculate wages, training duration or investment returns.
07 / Read the candidate responsibly
Station S5 sets the cycle at 1.35 min.
8 required · 6 available · 2 additional. Lower bound 7.
Ceiling if every station is staffed: 311 garments per shift.
8.65 work + 2.55 idle = 8 stations × 1.40 takt + 0.00 overload
01 / Longest station
Read the operation IDs in the highest stack, then observe those tasks at the workstation. Check handling, quality checks and machine time as well as sewing time. A balanced chart can still describe an impossible physical layout if an operator must cross the line, change machines repeatedly or wait for material.
02 / Staffing
The additional-operator answer is the difference between the feasible heuristic station count and your available crew. It is not a claim that this many hires will produce the requested quantity. Relief cover, learning, attendance, maintenance and skill availability can change the practical requirement.
03 / Capacity
Net minutes divided by the bottleneck cycle is a steady-state deterministic capacity ceiling for a fully staffed candidate. It excludes start-up, empty-line fill, variability, transfer delays and defects unless already embedded in the inputs.
04 / Idle and overload
Save A before changing demand or operation times. Compare the same product, allowance convention and time boundary. A higher balance percentage can accompany lower output if the bottleneck cycle lengthens. The gaps under takt are the idle; the band above it is overload.
01 / Method source, opened 30 October 2026
Takt Time · Lean Enterprise Institute
Defines takt as available time divided by demand, the denominator of this page.
On the map: the dashed takt line, net minutes divided by target.
08 / Provenance: inputs and sources
These are the illustrative defaults the page starts from. Choose Your inputs to see the same register with your numbers. Point at a row to see which figures it moves.
| Input | Value shown | Status and basis | What to replace it with |
|---|---|---|---|
| Net production time | 420 minchangedEdit ↑ | Illustrative. A teaching production window after excluded breaks. | Replace with: Your line's planned available time, with its boundary documented. |
| Target output | 300 garmentschangedEdit ↑ | Illustrative. A round batch chosen to demonstrate station packing. | Replace with: Demand due within the same production window. |
| Operation bulletin | 12 operations, 8.65 minchangedEdit ↑ | Illustrative. A simplified T-shirt route assembled for this instrument. The total is the sum of the editable SMVs. | Replace with: A measured and approved operation bulletin for one product. |
| Available operators | 6 operatorschangedEdit ↑ | Illustrative. A deliberately short starting crew to expose a staffing gap. | Replace with: Operators available to the line, excluding shared support. |
| Routing | Respect predecessorschangedEdit ↑ | Illustrative. The entered links form a simplified assembly sequence. | Replace with: Engineering-approved task dependencies, checked on the actual garment. |
| One operator per station | Fixed | Model assumption. Operations cannot be split; equipment and skills are unconstrained. | Replace with: a feasible machine, skill and workstation plan before implementation. |
Defines takt as available time divided by demand, the denominator of this page.
Lean Enterprise Institute. Publication date not stated; opened 2026-10-30. Method reference only; no T-shirt timing is sourced to this publication.
t = 420 ÷ 300 = 1.40 min
Takt = net minutes ÷ target garments. Largest-candidate assignment respects entered predecessors unless flexible routing is selected. Each station has one operator; tasks cannot be split. Work + idle = station count × takt + overload. Balance efficiency uses the largest station load as the cycle denominator.
A planning aid. Not investment, legal or tax advice. Verify inputs and boundaries before an operational decision.
Defines the operator balance chart: vertical bars of work per operator against takt.
Lean Enterprise Institute. Publication date not stated; opened 2026-10-30. Method reference only; no T-shirt timing is sourced to this publication.
Bar = work per station; dashed line = takt 1.40 min
Do not use the illustrative route to set a worker's target. Spare operators remain outside the candidate assignment rather than being shown as if they automatically improve throughput.
Describes the largest-candidate rule used for the assignment.
INFORMS Transactions on Education. Published online 2022-08-25; opened 2026-10-30. Method reference only; no T-shirt timing is sourced to this publication.
Stations = 8; E = 80.1%
Equal-sized tasks keep their input order, so the result is reproducible. When the available crew cannot staff every station, this instrument withholds available-line capacity. The aggregate labour ceiling is a separate arithmetic check, not a substitute for a route. Review cycle, staffing, feasibility and work content together. The chart, assignment table, scenario URL and CSV retain enough detail for another engineer to reproduce the arithmetic.
Places the balance of one line inside overall equipment effectiveness.
Covers OEE, line balancing and lean flow. A programme reference, not a claim of a released paper.
Explains why measured SMVs must come before any assignment.
Covers performance measurement from the first shift. A programme reference, not a claim of a released paper.
Explains why a balanced chart still needs skills on the floor.
Covers skills and supervision. A programme reference, not a claim of a released paper.
09 / Close on the floor
A station plan is a hypothesis. Reconcile the operation bulletin, machine availability and skill matrix, then observe whether the work fits the same net time boundary.
2 of 4 picks beaten in
Nothing is confirmed. The chart is an arithmetic hypothesis.
One check done. Treat every station as provisional.
Half confirmed. The remaining checks could still move the bottleneck.
Three checks done. Observe one shift before moving anyone.
All four done. The assignment is ready for a floor trial, not a hiring promise.
The model counts one operator per station. It excludes absenteeism, relief cover, variable performance, breakdowns, rework and transfer time unless you include them in the measured inputs. A task above takt requires a process change or a separately validated parallel arrangement.
09 / Rebalance and staff the line
Then staff the line.
2 of 4 checks confirmed: the stations settle toward the 1.40 min takt line. A target picture, not a result.