What BOM Compare does
BOM Compare takes two revisions of a bill of materials (BOM) and shows what changed between them. Parts are matched by part number, and each part is marked Added, Removed, Changed or Unchanged, so you can see the effect of a revision before you update an assembly or place an order.
It compares flat tables. It does not compare CAD geometry, rebuild assembly hierarchy or approve substitutions.
Inputs and outputs
- Input
- A “Before” and an “After” BOM, each a UTF-8 CSV or TSV file of up to 4 MB, or pasted CSV text. The first row is the header; you map the columns to Part number and Quantity (required) and Item, Description and Material (optional).
- Output
- A filterable comparison table with the status of every part, the quantity change (After minus Before) and the fields that changed. Export it as a CSV file.
How to compare two BOM revisions, step by step
- Export each BOM revision from your CAD, PDM or spreadsheet as CSV (UTF-8). In Excel, use “CSV UTF-8”.
- Choose the Before file and the After file, or paste the CSV text. You can also select “Try sample revisions”.
- Confirm the column mapping on both sides. Part number and Quantity must be mapped.
- Select “Compare BOMs”.
- Filter by Added, Removed, Changed or Unchanged, and read the quantity change and changed fields for each part.
- Select “Export comparison” to download the result as CSV, then review the change against your drawing change record before purchasing or assembly.
How parts are matched
- Added: the part number appears only in the After BOM. Removed: it appears only in the Before BOM.
- Changed: the part number is in both BOMs and its quantity, description or material differs. Unchanged: all three match.
- Part numbers are matched exactly and are case-sensitive. A part that shows as both removed and added is often a whitespace, case or O/0 difference.
- Each part number must appear once per BOM. The tool stops and names the duplicate so you can combine or distinguish the rows first.
- Quantities must be plain non-negative numbers with a dot decimal separator, up to six decimal places, with no units or thousands separators.
Supported file formats
- CSV and TSV, UTF-8 encoded, up to 4 MB per file, or text pasted into the page.
- Excel workbooks are not read directly. Save the sheet as CSV UTF-8 first.
- Output: CSV (bom-comparison.csv).
Frequently asked questions
What does the BOM Compare tool do?
It compares two BOM revisions by part number and lists the parts that were added, removed or changed, together with the quantity change. You can export the comparison as CSV.
Is BOM Compare free?
Yes. BOM Compare is one of MST’s free engineering tools, and it includes sample revisions you can try first.
Which file formats does BOM Compare accept?
UTF-8 CSV and TSV files of up to 4 MB each, or pasted CSV text. Excel files are not read directly, so save the sheet as CSV UTF-8 first.
Which fields are compared?
Parts are matched by part number. For parts present in both BOMs, the tool compares quantity, description and material. Map the Description and Material columns on both sides if you want those changes shown.
Why does a part appear as both removed and added?
Part numbers are matched exactly and are case-sensitive. Check for extra spaces, different capitalization, or the letter O versus the digit 0 in the identifier.
Why does the tool refuse my file?
The usual causes are a duplicate part number within one BOM, a missing part number, a quantity with units or a thousands separator, or a file that is not UTF-8. The message names the row or part so you can fix it.
Does BOM Compare compare CAD models?
No. It compares flat BOM tables only. It does not compare geometry, rebuild assembly hierarchy or approve part substitutions.
How do I get a BOM out of a drawing first?
Use the free Drawing to BOM tool to read the parts table from a PNG, JPEG or PDF drawing, then export it as CSV.
About MST
This is a free tool from MST. MST AI Engineer has three modules: drawing to model, layout and connections, and mechanical assembly AI, which takes a P&ID gas-line diagram plus approved PDM parts and equipment rules and builds a native, editable SOLIDWORKS assembly, starting with semiconductor gas equipment. Learn about MST AI Engineer.