What is Scrap Rate? Definition & Manufacturing Examples

What is Scrap Rate?

Scrap rate is the percentage of total production output that is defective beyond repair and must be discarded. Scrapped units cannot be reworked or salvaged to meet product specifications — they represent a complete loss of the raw materials, labor, energy, and machine time invested in producing them. Scrap rate is a key quality and cost metric that directly impacts material costs, capacity utilization, and delivery reliability.

How Scrap Rate Works

Scrap rate is calculated with a simple formula:

Scrap Rate = (Scrapped Units / Total Units Produced) x 100

Scrap can occur at any stage of manufacturing. Common causes include: tool wear that produces out-of-tolerance dimensions, material defects such as voids or inclusions in castings, operator errors in setup or programming, machine malfunctions that damage parts mid-cycle, and process variations that exceed control limits.

Scrap is categorized by cause to enable root cause analysis and corrective action. Tracking scrap by machine, operator, material lot, and operation identifies patterns. If 80 percent of scrap at the grinding operation occurs on Machine G-3, the problem is likely the machine — worn spindle bearings, poor coolant flow, or misalignment. If scrap spikes after a new material lot is introduced, the raw material supplier needs attention.

The financial impact of scrap extends beyond the material cost. A scrapped unit at the final operation has consumed all upstream labor, machine time, and overhead — making late-stage scrap far more expensive than early-stage scrap. A raw material defect caught at receiving inspection costs only the material price. The same defect caught at final assembly has accumulated the full manufacturing cost.

Scrap Rate Example

A precision turned parts manufacturer produces 50,000 parts per month across 15 CNC lathes. Monthly scrap report: 750 parts scrapped at turning (1.5 percent), 200 parts scrapped at secondary milling (0.4 percent), and 150 parts scrapped at plating (0.3 percent). Total scrap: 1,100 parts, or 2.2 percent overall scrap rate.

Average material cost per part is $4.50. Average accumulated manufacturing cost at scrap point: turning scrap at $7.00 per part, milling scrap at $12.00 per part, and plating scrap at $18.00 per part.

Monthly scrap cost: (750 x $7) + (200 x $12) + (150 x $18) = $5,250 + $2,400 + $2,700 = $10,350. The plating operation scraps the fewest parts but accounts for 26 percent of scrap cost because its accumulated manufacturing cost is highest.

Investigation reveals that 60 percent of turning scrap traces to tool breakage on one material grade. Installing tool wear monitoring reduces turning scrap from 750 to 200 parts per month. Monthly scrap cost drops to $5,450 — a 47 percent reduction from a single improvement targeting the highest-volume scrap category.

Why Scrap Rate Matters for Production Scheduling

Scrap rate directly affects scheduling in two ways. First, the scheduler must inflate production order quantities to ensure enough good units are produced. If the customer needs 1,000 pieces and the historical scrap rate is 5 percent, the production order quantity should be approximately 1,053 (1,000 / 0.95). Under-estimating scrap leads to short shipments; over-estimating wastes materials and capacity.

Second, scrap consumes capacity that was scheduled for productive output. If a machine is loaded for 40 hours of work but scrap wastes 3 hours of that capacity, only 37 hours of good output are produced. The schedule becomes overloaded and downstream operations are starved.

Scheduling software like Resource Manager DB (RMDB) can apply scrap factors to production orders automatically, increasing order quantities and adjusting capacity loads to reflect realistic yields. This ensures the schedule is achievable and customer quantities are met without last-minute additions.

Related Terms

• First Pass Yield — The complementary metric measuring the percentage of units that pass quality checks without scrap or rework
• Rework — Defective units that can be corrected, unlike scrap which is a total loss
• Overall Equipment Effectiveness — The composite metric where scrap rate directly impacts the quality component

Frequently Asked Questions

Learn more in our complete manufacturing glossary or production scheduling guide.