BOM Comparison Worksheet: Compare Two BOM Revisions
When a BOM goes from Revision A to Revision B, you need to know exactly what was added, removed or changed in quantity, and what it does to cost. This worksheet lets you key or paste the two revisions side by side and gives the delta per line and in total.
| Component | Description | UoM | Qty Rev A | Qty Rev B | Unit cost | Qty change | Cost Rev A | Cost Rev B | Cost delta | |
|---|---|---|---|---|---|---|---|---|---|---|
0 | $18 | $18 | $0 | |||||||
2 | $0 | $1 | $0 | |||||||
0 | $1 | $1 | $0 | |||||||
-3 | $2 | $0 | -$2 | |||||||
3 | $0 | $3 | $3 | |||||||
0 | $0 | $0 | $0 |
Enter a component with Rev A quantity 0 for an added line, and Rev B quantity 0 for a removed line. Use one unit cost per component so the delta reflects quantity changes only. If the cost also changes between revisions, add a second row for the same component and note it.
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How to use the BOM comparison worksheet
List every component that appears in either revision, one per row. Enter its quantity per parent in Revision A and Revision B, using zero where the component does not exist. Enter a unit cost, typically the standard cost or latest purchase price. The sheet calculates the quantity change, the extended cost in each revision and the cost delta, then totals them and shows the percentage cost change. Export to Excel to share with the change control board or attach the CSV to the ECO. Start from a BOM export from your ERP so that component numbers match exactly.
- Use identical component numbers in both columns, no retyping
- Zero in Rev A means added, zero in Rev B means removed
- Compare at the same level and the same unit of measure
- Sort by cost delta to find the lines that matter
What counts as a BOM change
A real comparison covers more than quantity. Typical differences are added or removed components, quantity per changes, unit of measure changes, substitutes and alternates, scrap or yield factors, reference designators in electronics, operation assignment of a component, and effectivity dates. This worksheet focuses on quantity and cost because those drive the financial and planning impact. For the other attributes, add notes to the description column or compare the exported ERP tables in a spreadsheet. In SAP the relevant data sits in the STKO and STPO tables, and in other systems the equivalent BOM header and component tables.
Worked example
The sample rows show a Revision B that adds two O-rings, swaps a steel plug for a stainless one and leaves the rest unchanged. The extended cost of the O-rings rises by 0.24, removing the three steel plugs saves 1.65, and adding three stainless plugs costs 3.30. The net effect is a small increase. That is the kind of result a change board needs: a clear statement that the revision costs slightly more per assembly, so the benefit (for example corrosion resistance) can be weighed against it. Multiply the per-unit delta by annual volume for the full financial picture.
Common mistakes
Comparing different BOM levels, such as a single-level BOM on one side and a flattened multilevel BOM on the other, produces false differences. Mixing units of measure (meters versus millimeters) causes quantity errors that look like real changes. Forgetting that a phantom assembly can hide component changes is another trap. Finally, comparing cost with different cost bases (standard in one, last purchase in the other) mixes price effects with design effects. Fix the cost basis first, then compare designs, then separately review price variances.
Frequently Asked Questions
How do I compare two BOMs in Excel?
List all components from both BOMs in one column, then use lookups or this worksheet to show each revision quantity side by side. Subtract to get the change. Rows where one side is zero are added or removed components.
Can I paste a BOM export into this worksheet?
You can enter rows manually, and exporting to Excel lets you extend the sheet with your own data. Keep component numbers consistent between revisions so that changes are not reported as separate additions and removals.
Does it compare multilevel BOMs?
It compares whatever rows you enter. For a multilevel comparison, explode both BOMs to the same depth and level first, or compare each sub-assembly separately, then roll the deltas up.
Why does cost delta ignore price changes?
It uses a single unit cost per component so the delta shows the effect of design change alone. Price changes are a purchasing matter, and mixing both makes it unclear what the engineering change actually cost or saved.
If you compare BOMs by hand often, Netray can help automate revision comparison straight from your ERP BOM tables with a read-only query. The worksheet is free to use as it is.
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