Ask most factories what poor quality costs them and they will quote the scrap figure. That is usually the smallest part of the story. Rework hours, extra inspection, expedited freight, sorting at the customer's site, warranty claims, management time and lost orders add up to far more. Cost of quality (COQ) puts a number on all of it, so quality problems can be discussed in the language management understands: money.
The four categories
Prevention costs
Money spent to stop defects happening: quality planning, FMEAs, training, error-proofing devices, preventive maintenance of critical equipment, supplier development, process capability studies and design reviews.
Appraisal costs
Money spent checking whether products are good: incoming, in-process and final inspection, testing, laboratory costs, calibration, inspection equipment and audits.
Internal failure costs
Costs of defects found before the product reaches the customer: scrap, rework labour and materials, re-inspection, downgrading, investigation time, lost machine capacity and the overtime needed to replace scrapped parts.
External failure costs
Costs of defects found by customers: returns and replacements, sorting at the customer's site, warranty claims, penalties and chargebacks, expedited freight, field repair visits, complaint handling time and — hardest to measure — lost business and reputation.
Prevention and appraisal are the cost of good quality. Internal and external failure are the cost of poor quality.
The hidden costs
Many failure costs never appear as a line in the accounts:
- Machine time used to remake scrapped parts — capacity that could have produced saleable output.
- Planning disruption when jobs are re-run.
- Extra inventory held "just in case" because yields are unpredictable.
- Engineers and managers in investigations and customer meetings.
- Premium freight to recover late deliveries.
- Discounts given to keep an unhappy customer.
You don't need to calculate these precisely, but include reasonable estimates. Leaving them out makes poor quality look cheaper than it is.
Collecting the data
COQ doesn't need a special accounting project. Start with sources you already have:
- Scrap records — quantity × material and processing cost to the point of scrap.
- Rework records — hours × labour and machine rate, plus extra material.
- Nonconformance reports — each with an estimated cost.
- Complaint records — sorting charges, replacements, freight, credit notes.
- Inspection staff and lab costs — from payroll and budgets.
- Calibration and test equipment costs.
- Training and quality planning time — estimated.
The biggest improvement is usually making sure scrap and rework are recorded at the point they happen, with a reason and the job they belong to. When scrap is only counted at month-end from bins, costs can't be traced to causes.
A simple worked example
A mid-sized machining company estimated its monthly quality costs:
- Prevention: training and PFMEA time — modest.
- Appraisal: three inspectors, CMM operation and calibration — moderate.
- Internal failure: scrap and rework — the largest single item, about twice appraisal.
- External failure: two customer sorting charges, replacement parts and air freight — smaller than internal failure but growing.
The total was several times what the management team had assumed, because they had only ever looked at the scrap value. More than 70% of COQ was failure cost; less than 5% was prevention. That ratio is typical — and it's the opportunity.
Using COQ to drive improvement
- Pareto the failure costs by product, process, defect type and customer. A handful of problems usually account for most of the cost.
- Pick the top two or three and run root cause analysis.
- Invest in prevention — error-proofing, fixtures, maintenance, training — and estimate the payback from the failure cost it will remove.
- Track the result month by month.
Prevention investments often look expensive in isolation. Next to the failure cost they eliminate, they're usually easy decisions.
Reporting COQ
Present COQ monthly, both as an absolute amount and as a percentage of sales or production cost, so it can be compared over time as volume changes. Show the split between the four categories and the top failure items. Avoid turning it into a blame exercise between departments — the purpose is to find where money is being lost and fix the cause.
What good looks like
Over time, mature companies see total COQ fall while prevention spending rises as a share. Appraisal costs often fall too, as capable processes and error-proofing reduce the need for heavy inspection. The shift from "inspect and fix" to "prevent" is the long-term goal.
Common mistakes
- Counting only scrap material.
- Waiting for perfect accounting data before starting.
- Reporting COQ without acting on the top items.
- Cutting prevention budgets to save money in the short term.
- Using COQ to blame individuals or departments.
How software helps
When scrap, rework, nonconformances and complaints are recorded digitally with job, reason and cost, COQ reports build themselves — by product, process, customer and month — and the biggest losses are visible without spreadsheets. See NCR management software and production costing software.
Talk to us about seeing your real cost of quality.
Getting finance and quality to agree
COQ numbers are only credible if finance accepts the method. Agree in advance which rates are used for labour and machine time, how material is valued at the point of scrap, and which categories are estimated rather than measured. Document the assumptions on one page and keep them stable, so month-to-month changes reflect real improvement rather than a change in method.
Frequently asked questions
What is cost of quality?
The total cost of preventing defects, checking for them, and dealing with the defects that happen — inside the factory and after products reach customers.
What is cost of poor quality (COPQ)?
The part of cost of quality caused by failures: scrap, rework, re-inspection, returns, warranty, penalties and lost business. It's the money you could recover by preventing defects.
How accurate does the calculation need to be?
Not very, at first. A reasonable estimate built from scrap records, rework hours and complaint costs is enough to show where the money goes and prioritise action.
Is it good to spend more on inspection?
Inspection is appraisal cost — it catches defects but doesn't prevent them. Shifting spending towards prevention usually reduces total cost of quality.
How often should we report cost of quality?
Monthly is common, with the biggest failure costs reviewed in management meetings alongside the actions to reduce them.
