What Is Capacity Planning?
Capacity planning is the process of determining whether your production system can meet customer demand — and what to do when it cannot. It answers the most fundamental question in operations: can we make what we need to make, when we need to make it?
Done well, capacity planning prevents overtime crises, missed deliveries, and expensive emergency actions. Done poorly (or not at all), it leads to chronic firefighting, bloated inventory, and broken customer promises.
Key Concepts
Rated vs. Demonstrated Capacity
| Type | Definition | Use |
|---|---|---|
| Rated (Theoretical) | Maximum output if everything ran perfectly: no downtime, no changeovers, no defects, 100% speed | Upper bound. Useful for investment decisions. |
| Demonstrated (Effective) | What you actually produce, accounting for OEE losses: downtime, speed loss, scrap | Planning basis. This is the number you schedule against. |
Never Plan to Rated Capacity
Planning to theoretical maximum is the #1 capacity planning mistake. If your machine is rated at 100 units/hour but your OEE is 65%, your effective capacity is 65 units/hour. Plan to demonstrated capacity, then work on improving OEE to close the gap. Use the capacity utilization calculator.
Bottleneck Capacity
Your system capacity equals the capacity of your bottleneck — the slowest step in the process. It does not matter if every other step can do 200 units/hour; if the bottleneck does 80, your system does 80. See Theory of Constraints.
Capacity Buffer
Running at 100% utilization sounds efficient but creates exponentially growing queue times. A 15-20% buffer absorbs normal variability (breakdowns, absenteeism, demand spikes) without missing deliveries. The math is clear: at 90% utilization, queue times are 3-5x longer than at 75%.
Every rate is the page's own. Cut 120, Weld 80, Paint 150 and Pack 200 units/hr come from the flow diagram under "Bottleneck Capacity"; 80/hr as the system capacity is that diagram's caption; 65% OEE is the "Never Plan to Rated Capacity" callout; 85% is the stat grid's ideal utilisation; the 15–20% buffer is the "Capacity Buffer" section. The arithmetic is the page's own formulas applied to the page's own bottleneck, which the page itself never does: Effective Capacity = Rated × OEE gives 80 × 0.65 = 52/hr demonstrated at the weld, and holding the buffer gives 52 × 0.85 = 44.2/hr plannable, or 52 × 0.80 = 41.6/hr at the other end of the range — a reserve of 7.8–10.4/hr. OEE loss at the constraint is 28/hr. The average, 137.5/hr, is (120 + 80 + 150 + 200) ÷ 4 — the number a spreadsheet reaches for, and the one the page warns against, since system capacity is the smallest step rather than the mean of them. The headroom above the constraint is (120 − 80) + (150 − 80) + (200 − 80) = 230/hr. As ratios, 44.2 is 55% of 80, 32% of 137.5 and 22% of 200.
The Three Planning Horizons
| Horizon | Timeframe | Decisions | Tools |
|---|---|---|---|
| Strategic | 1-3 years | New equipment, new lines, facility expansion, outsourcing | Demand forecasting, financial modeling |
| Tactical | 1-6 months | Shift schedules, overtime planning, temporary labor, inventory buffers | Throughput analysis, safety stock |
| Operational | Daily-weekly | Job scheduling, line balancing, changeover optimization | Takt time, hour-by-hour boards |
Capacity Planning Process
Quick Capacity Calculations
| Calculation | Formula | Tool |
|---|---|---|
| Effective Capacity | Rated Capacity × OEE % | OEE Calculator |
| Required Takt Time | Available Time ÷ Demand | Takt Calculator |
| Operators Needed | Total Work Content ÷ Takt Time | Line Efficiency |
| Utilization % | Actual Output ÷ Max Possible Output | Utilization Calculator |
| WIP Required | Throughput × Lead Time | Little's Law |
✅ Good Capacity Planning
- Plans to demonstrated (OEE-adjusted) capacity
- Maintains 15-20% buffer for variability
- Exhausts operational improvements before capital
- Reviews capacity monthly against rolling forecast
❌ Capacity Planning Failures
- Plans to rated/theoretical capacity
- Runs at 95%+ utilization (queue time explosion)
- Buys equipment before improving OEE
- Only checks capacity during annual budget
🎯 Key Takeaway
Capacity planning is not a spreadsheet exercise done once a year — it is a continuous practice that connects demand to demonstrated capability. Always plan to OEE-adjusted capacity, always maintain a buffer, and always improve the bottleneck before buying new equipment. The cheapest capacity is the hidden capacity you already own — find it with OEE tracking, SMED, and line balancing.
Interactive Demo
Three work centres, each with its own available hours, efficiency and demand. Move any of them and watch where utilization lands — and which one turns red first.
Stop reading, start modeling
Model your process flow, run simulations, optimize staffing with TOC math, and test your knowledge with 107 interactive checks — all in one platform.