BOM Accuracy Calculator
BOM accuracy is the share of bills of material that match what is really built. Weak BOMs produce wrong MRP requirements, shortages and inflated or understated cost. This calculator turns a small audit into BOM accuracy, line accuracy and a rough cost to reach your target.
Your numbers
Number of BOMs physically or technically checked against the build.
Wrong part, quantity, UoM, scrap factor or missing component.
Your results
Estimates extrapolate from your audit sample to the full BOM population. Use a stratified sample and treat the result as a planning range, not a precise count.
Rework cost vs target accuracy
Sweeps Target BOM accuracy from 90 to 100, holding your other inputs fixed.
Want PLM to ERP BOM differences found automatically?
Optional: we can review a sample of BOM exports and show where the structures disagree.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Audit a sample of BOMs by comparing the ERP structure to the engineering release and the actual build or kit. Count a BOM as correct only if every line is right: part, quantity, UoM, scrap and effectivity. Enter the counts, the total active BOMs, your target and your rework assumptions. The chart shows how the cost of cleanup grows as the target moves toward 100 percent, which helps you choose a realistic goal.
The formulas
BOM accuracy equals correct BOMs divided by audited BOMs, times 100. Line accuracy equals one minus error lines divided by audited lines. Both matter: a BOM with a single bad line still fails the BOM measure, but the line measure shows how widespread the errors are. Classic MRP guidance, for example in Oliver Wight style class A criteria, cites targets of around 98 to 99 percent or better for BOM accuracy, so the default target here is 98.
- BOM accuracy = correct BOMs / audited BOMs
- Line accuracy = 1 - error lines / audited lines
- BOMs to fix = total BOMs x (target - actual)
- Cost = BOMs to fix x hours x rate
Worked example
With 46 of 60 BOMs correct, BOM accuracy is about 76.7 percent, while 58 bad lines out of 1,450 gives line accuracy near 96 percent. Against a 98 percent target on 3,200 active BOMs, about 680 BOMs need fixing. At 1.5 hours and 55 dollars per hour that is roughly 56,000 dollars. The gap between the two accuracy figures shows that errors are spread thinly across many BOMs rather than concentrated in a few.
Common mistakes
Auditing only new products skews results optimistic, because older BOMs carry years of unreleased changes. Counting a BOM correct when only the item list matches ignores quantity, UoM and scrap errors. Using engineering BOMs instead of manufacturing BOMs in the sample misses the structure MRP actually explodes. Finally, cleanup without an engineering change discipline lets accuracy decay after the project ends.
Frequently Asked Questions
What is a good BOM accuracy percentage?
Common MRP guidance targets about 98 percent or higher at BOM level. Many plants start well below that. Track the trend and the cause of errors rather than only the headline figure, and set a target that fits your product complexity.
How many BOMs should I audit?
A sample of 50 to 100 BOMs, stratified by product family and age, is practical. Smaller samples give wide uncertainty, so treat results from fewer than 30 BOMs as indicative only.
What counts as a BOM error?
Any difference from the validated build: wrong or missing component, wrong quantity per, wrong UoM, wrong scrap or yield factor, wrong effectivity date, or an operation linkage that supplies material at the wrong step. Define the list in advance and apply it consistently.
Is BOM accuracy the same as inventory record accuracy?
No. BOM accuracy measures structure data, while inventory record accuracy compares counted stock to the system quantity. Both feed MRP, and both are usually reported together in planning health reviews.
If you would like BOM comparisons between PLM and ERP run automatically and flagged by difference type, we can build that as a read-only check on your own systems.
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