Why "Just Multiply SMV by Cost Per Minute" Isn't Enough

A merchandiser sends a CM quote of $1.04 per piece. The buyer's costing team asks one question: how did you get that number. If the honest answer is "our costing sheet has always used $0.055 per minute," the negotiation is already lost, because that figure was never rebuilt against this season's utility bills, this line's actual efficiency, or this factory's current headcount.

Cost per minute (CPM) is not a constant. It moves every time rent, gas tariffs, or line efficiency moves, and a factory that cannot show its build-up loses the argument before it starts, the same way a factory that cannot show its SMV study sheet loses on the minutes side.

The Two Numbers a CM Price Is Built From

Cost per minute (CPM) = Total monthly factory cost / Total available minutes per month
CM price (per piece)  = SMV x CPM

Total available minutes is not a theoretical number. It is:

Available minutes = Operators on payroll x Working minutes per day x Working days x Line efficiency

Line efficiency here is the plant's actual achieved efficiency (from your factory KPI dashboard), not the target the sales team wishes were true.

What Goes Into "Total Monthly Factory Cost"

Cost head

Typical share of CPM

Notes

Direct labor (wages, wage-linked benefits)

45-55%

Sewing, cutting, finishing operators

Indirect labor (supervisors, QC, maintenance)

10-15%

Not tied to a single SMV but must be absorbed

Utilities (power, gas, water)

8-12%

Volatile; recalculate quarterly

Factory rent/depreciation

8-10%

Fixed regardless of order volume

Admin and compliance overhead

5-8%

Compliance audits, certifications

Consumables (needles, thread waste, maintenance parts)

3-5%

Often under-budgeted

Most costing sheets that go stale do so because utilities and consumables are copied forward unchanged for a year while everything else is updated.

Worked Example: A 400-Operator Line

Inputs

  • Total monthly factory cost: $185,000

  • Operators on payroll: 400

  • Working minutes per day: 480

  • Working days per month: 26

  • Achieved line efficiency: 62%

Step 1: Available minutes

400 x 480 x 26 x 0.62 = 3,096,576 minutes per month

Step 2: Cost per minute

$185,000 / 3,096,576 = $0.0597 per minute

Step 3: CM price for an 18.9-minute SMV garment

18.9 x $0.0597 = $1.128 per piece

If the same factory quoted using last year's efficiency of 68% instead of this year's actual 62%, available minutes would be overstated and CPM understated by about 9%, which on a 50,000-piece order understates true cost by roughly $5,000, a margin gap that shows up as a loss three months into shipping, not at costing.

From CM Price to FOB Price

CM is one line in the full costing sheet, not the whole quote:

FOB price = Fabric cost + Trims cost + CM price + Wastage allowance + Freight/duty share + Profit margin

Cost component

Who controls it

Where it's derived

Fabric

Merchandising/sourcing

Consumption x fabric rate

Trims

Merchandising/sourcing

BOM cost sheet

CM

Industrial engineering

SMV x CPM

Wastage

Production/cutting

Marker efficiency, covered in RMG cutting process control

Margin

Commercial/finance

Factory policy, typically 8-15% on FOB

Garment Costing Checklist

  • CPM rebuilt against actual (not target) line efficiency, at least quarterly

  • Utility and consumable costs updated, not carried forward unchanged

  • Indirect labor allocated across lines by headcount or minutes, not ignored

  • SMV traceable to a signed study sheet before it enters the costing sheet

  • FOB build-up shows fabric, trims, CM, wastage and margin as separate lines, not one lump sum

  • Quoted CPM re-validated against the actual month-end factory cost report

Final Word

A CM price is only as trustworthy as the two numbers that built it: the SMV and the cost per minute. Get the SMV wrong and you have already seen what an eighteen-second error costs a 50,000-piece order. Get the cost-per-minute build-up wrong and the same order can be quoted a full nine percent under true cost without anyone noticing until the line has already run. Rebuild CPM from actual monthly cost and actual achieved efficiency, not from a spreadsheet nobody has touched since last season.