WIP (Work in Progress) Estimator
Calculate holding days and inventory capital tied up in Work in Progress across sewing line operations.
WIP is cash sitting on the floor in unfinished form. Holding days translate a pile of pieces into the language managers use: how many days of production are stuck inside the line, and how much money that pile represents. Track it daily, and it becomes an early warning system: WIP that grows while output stays flat means input is outrunning the line, and trouble is building before it shows up in the shipment report.
What is WIP (Work in Progress)?
Work in progress is every garment piece that has started production but is not yet finished: bundles waiting at workstations, pieces moving between operations, and pieces sitting in rework. It is the inventory inside the line, as opposed to raw fabric in the store or finished goods in the warehouse. Every factory carries some WIP, because work must wait briefly between operations, but the amount matters enormously. A line with 3 days of WIP has three days of production that cannot ship, three days of cash locked in cloth and labour, and three days during which a defect found at final inspection may already exist in hundreds of pieces still on the line.
Holding days express that pile as time: total WIP pieces divided by daily output. The result answers the question a manager actually asks, which is not how many pieces are on the floor but how long they will take to clear. The optional money figure multiplies the pile by a per-piece FOB value, turning the same pile into capital at stake. Together the two numbers let a factory compare lines, days, and styles on equal terms: a 2,700-piece pile is a small problem on a 2,700-piece-a-day line and a serious one on a 900-piece-a-day line, and only the days figure shows the difference.
Formula
WIP Holding Days = Total WIP Pieces / Daily Output Rate WIP Monetary Value = Total WIP Pieces × FOB Value per Piece
- Total WIP Pieces: started but unfinished pieces physically on the line at count time. Must be zero or more.
- Daily Output Rate: finished pieces per day at the line current pace. Must be greater than zero, or the days figure has no meaning.
- FOB Value per Piece: optional. Leave it blank and the money figure shows as not available; enter it and the calculator values the whole pile at that per-piece figure.
- Result: holding days shown to one decimal place, money shown to two decimals with thousands separators.
How to Calculate
- Count line WIP at a fixed time, ideally shift start: bundles at workstations, pieces between operations, and pieces in rework. Exclude finished goods and uncut fabric.
- Enter the daily output rate: finished pieces per day at the current pace, not the target pace, because holding days measure how fast the pile actually clears.
- Optionally enter a per-piece FOB value to price the pile. Remember the result is capital value at FOB, not production cost spent so far.
- Read holding days and the money figure. Log both daily: a single reading is a snapshot, but the trend is the management signal.
- Act on the trend. Days rising while output is flat means input is outrunning the line: cut input, add capacity at the bottleneck, or both. Days falling sharply can mean starvation risk if input is cut too far, so check that workstations are not waiting for work.
Example
Take the same illustrative line used across the production tools, producing 900 pieces a day. A morning count finds 2,700 pieces of WIP on the line. Holding days = 2,700 / 900 = 3.0 days. At an illustrative FOB of 6.50 dollars per piece, monetary value = 2,700 × 6.50 = 17,550 dollars of capital sitting unfinished on the floor. If the line tightens bundle discipline and brings WIP down to 1,800 pieces, holding days fall to 1,800 / 900 = 2.0 days and the tied-up value falls to 1,800 × 6.50 = 11,700 dollars, freeing 5,850 dollars of working capital without producing a single extra piece.
The same numbers also show how WIP grows. Recall the floor-control example from the sibling tools: the line targets 900 pieces but actually makes 810, a shortfall of 90 pieces a day. If cutting keeps feeding 900 pieces a day into the line, the pile grows by 90 pieces daily, or 540 pieces over a 6-day week, and holding days creep up even though nobody made an obvious mistake. That is why WIP tracking belongs next to the Target vs Actual Calculator on the daily report: the variance explains why the pile moved, and the pile shows what the variance is costing in cash and lead time. If output later rises to 1,000 pieces a day, the same 2,700-piece pile clears in 2,700 / 1,000 = 2.7 days, which is the other way to cut holding days: faster output, not just less input.
Assumptions
This calculation is a snapshot: it assumes the counted WIP and the daily output rate hold steady, so holding days are the time to clear the pile at the current pace, not a forecast that accounts for style changeovers or absenteeism. It assumes WIP is counted consistently, at the same time and with the same scope, every day; changing the count scope mid-week breaks the trend. The money figure assumes every WIP piece carries the full entered per-piece value, which overstates cost spent so far and is best read as capital at stake, as explained in the FAQs. Finally, there is no universal good number of holding days: judge your line by its own trend, its style complexity, and its buyer lead-time requirement.