Over-booking production capacity is one of the most destructive things a garment factory can do. It leads to delayed shipments, air freight costs, buyer penalties, and damaged relationships — all of which are preventable if capacity is calculated correctly before orders are confirmed. This guide explains how to calculate monthly capacity and use it as the foundation for order acceptance decisions.
The Capacity Calculation
Monthly production capacity is determined by how many minutes your factory can produce in a month, divided by the SAM of the garment you will be making. The available minutes depend on number of lines, operators per line, working hours per day, working days, and efficiency.
Monthly capacity (pieces) = (Lines × Operators per line × Working hrs/day × 60 × Working days × Efficiency %) / SAM Example: Lines: 5 Operators per line: 30 Working hours: 10 hrs Working days: 26 Efficiency: 65% Garment SAM: 15 minutes Total available minutes = 5 × 30 × 10 × 60 × 26 = 2,340,000 minutes Effective minutes = 2,340,000 × 0.65 = 1,521,000 minutes Monthly capacity = 1,521,000 / 15 = 101,400 pieces
Why Capacity Varies by Style
The same factory with the same lines and headcount produces vastly different quantities depending on the SAM of the style. A simple t-shirt at SAM 8 produces far more pieces per day than a structured jacket at SAM 45. This is why capacity must be planned style-by-style, not just as a fixed monthly unit number.
Capacity vs SAM — Same Factory, Different Styles
| Style | SAM | Monthly Capacity (5 lines, 30 ops, 65% eff, 26 days, 10 hrs) |
|---|---|---|
| Basic t-shirt | 8 min | 190,125 pieces |
| Polo shirt | 13 min | 116,923 pieces |
| Woven shirt | 20 min | 76,050 pieces |
| Chino trouser | 28 min | 54,321 pieces |
| Structured jacket | 45 min | 33,800 pieces |
Building a Capacity Loading Plan
Once monthly capacity per style is known, a loading plan maps each confirmed order against available capacity week by week. If total committed order minutes exceed available minutes in any week, you are overbooked — and must either add overtime, reduce intake, or negotiate delivery dates before production starts.
Tip
Keep 15–20% of monthly capacity as buffer when booking orders. Actual efficiency is always lower than planned in the first days of a style, absenteeism varies, and machine breakdowns happen. A factory that books 100% of theoretical capacity will run late on almost every order.