BOM Table Conversion for Manufacturing RFQFrom Imperial Design BOM to Supplier-Ready Metric RFQ
A practical guide for engineers, buyers, and project managers who receive imperial design BOMs but need to send clean, metric, bilingual RFQ packages to global suppliers. Learn how to structure your Excel, add metric columns without breaking traceability, and use the BOM Batch Converter to avoid manual errors.
Table of Contents
Why BOM Conversion Matters
From design BOM to supplier-friendly RFQ data
Go to Section →Understand BOM Structure
Key columns and where units really live
Go to Section →Clean and Prepare the BOM
Normalize columns, units, and descriptions
Go to Section →Conversion Workflow
Excel formulas and BOM Batch Converter
Go to Section →Build Bilingual RFQ Tables
Column design for international suppliers
Go to Section →Common Mistakes
How BOMs get corrupted in conversion
Go to Section →Best Practices & Checklist
A repeatable RFQ preparation process
Go to Section →Why BOM Conversion Matters for RFQ
Many manufacturing RFQs start from a design BOM created in a CAD or PLM system using inch units. The original table is optimized for internal design work, not for suppliers who will quote and manufacture in metric. Column names are inconsistent, units are hidden inside descriptions, and key technical data is scattered in comments or drawing notes.
A supplier-facing RFQ BOM must do the opposite. It should be easy to filter, sort, and calculate in metric. Each line must keep a stable part number and revision while exposing clear quantities, dimensions, materials, and finishes in millimeters. Done well, BOM conversion reduces back-and-forth emails, eliminates copy-paste mistakes, and makes quotes from multiple suppliers directly comparable.
The key principle is simple: treat the imperial design BOM as a source of truth that is never overwritten. Instead of editing original columns, you add a clean metric view alongside them, drive conversions with formulas or tools, and use a locked RFQ sheet as the surface you send to manufacturers.
Understanding BOM Structure and Unit Columns
Typical Design BOM Columns
A design BOM usually focuses on identity and hierarchy. Common columns include Item, Part Number, Revision, Description, Quantity, Unit of Measure, and sometimes Drawing or Model links. These fields must remain untouched so that engineering, purchasing, and QA all reference the same identifiers.
For conversion work, you treat these columns as read-only. All unit changes and metric extensions happen in new columns so the source data can always be reconstructed or audited if a question arises later in the project.
Where Units Actually Live
In many real-world BOMs, unit-sensitive data appears in several places: free-text descriptions (for example, 2.500" x 3.000" plate), separate dimension columns, drawing references, or even a "Notes" field. Before you can automate conversion, you must identify which columns contain dimensions and decide how they will be represented in both inch and metric.
A robust RFQ layout usually isolates structured size fields (length, width, thickness, diameter, thread size) and keeps the description more human readable. This separation makes conversions repeatable and reduces the chance that a typo in a sentence changes a critical dimension.
Cleaning and Preparing the Source BOM
Preparation Steps Before Conversion
Copy the original BOM into a new workbook or worksheet dedicated to RFQ preparation. Protect or lock the original tab to prevent accidental edits. This ensures engineering can still reference the unmodified design BOM even after several RFQ rounds.
Use concise, consistent headers such as Part Number, Description EN, Qty, UoM, Material, Finish, Drawing, and Notes. Avoid having multiple columns that mean the same thing under slightly different names. Normalized headers make formulas and filters much easier to maintain across BOM revisions.
When possible, break compound descriptions into structured fields. For example, instead of a single "2.5" x 3.0" x 0.5" plate" string, create dedicated Length in, Width in, and Thickness in columns. You can still keep the original combined wording for readability, but conversions will be driven from the structured numeric fields.
Replace ambiguous unit strings such as "in.", "inch", and "inch(es)" with a consistent format, and make sure the UoM column clearly distinguishes between length, area, weight, and count. This avoids confusion when you add metric columns like Length mm or Mass kg later on.
BOM Conversion Workflow: Excel and BOM Batch Converter
Add Metric Columns and Automate Conversions
Once the structure is clean, you can safely introduce metric fields. The goal is to convert all unit-dependent values from inches to millimeters in a way that is traceable, easy to update, and consistent across hundreds of lines.
For each key size column such as Length in or Diameter in, create a matching Length mm or Diameter mm column immediately to the right. Use a distinct header style or color to signal that these columns are derived, not manually typed. For weight-based items, you can add Mass kg or Weight per piece kg columns if required by your suppliers.
In Excel, a typical conversion formula for a length stored in column F is =ROUND(F2*25.4, 2) , which converts inches to millimeters and rounds to two decimals. For BOMs with many mixed units, you can export the sheet and use the BOM Batch Converter to perform consistent conversions and then paste the results back into your RFQ view.
Decide how many decimal places you will keep for each dimension type and record that in a short note at the top of the RFQ sheet. For example, you might keep three decimals for precision machined features and one decimal for stock lengths. A documented rule prevents random rounding that can cause conflicts between RFQ, drawings, and CNC programs.
Before trusting the full sheet, spot-check the largest cost drivers such as machined housings, complex weldments, or high-volume fasteners. Compare converted dimensions to the original inch values, confirm that rounding behavior is acceptable, and verify that no text fields were accidentally converted as numbers.
Designing Bilingual RFQ Tables for Suppliers
When you send RFQs to suppliers in another country, language clarity becomes as important as unit clarity. A good RFQ BOM lets local engineers read detailed technical descriptions in their language while preserving the original English wording for cross-checking. The layout should also make it obvious which columns are for reference and which are for quoting.
A simple pattern is to keep one "engineering view" tab that contains extra columns and notes, and one "RFQ view" tab that surfaces only the fields suppliers need to quote: identity, quantities, dimensions, material, finish, and any special processing instructions. Both tabs read from the same underlying data so that updates remain synchronized.
| Column | Example Header | Purpose |
|---|---|---|
| Identity | Part Number, Rev | Stable reference across RFQ, drawings, and PO |
| Descriptions | Description EN, Description Local | Bilingual text so both sides can understand the same part without ambiguity |
| Quantities | Qty per Assembly, RFQ Qty | Differentiate design usage from one-time RFQ quantity |
| Dimensions | Length in, Length mm, Dia in, Dia mm | Show both imperial and metric for traceability and local machining |
| Material & Finish | Material (AISI/ASTM), Material Local, Finish | Bridge US standards and local equivalents plus coating or treatment |
| Commercial Fields | Currency, Target Lead Time, Supplier Notes | Make commercial expectations explicit in the same table |
You can keep the bilingual columns optional for internal use but strongly recommended for cross-border RFQs. Translating only the description column is usually enough when drawings carry detailed dimensional and tolerance information.
Common Mistakes in BOM Conversion
Overwriting Original Data
Replacing inch values with metric values in the same column destroys traceability. If a supplier questions a dimension, you have no easy way to show the original design intent or how the conversion was performed.
Mixing Rounding Rules
Using different decimal places or rounding directions line-by-line makes it impossible to tell whether a difference comes from design or random spreadsheet behavior. Always define a clear rounding policy and apply it consistently.
Converting Text Instead of Numbers
When numeric-looking strings are stored as text, formulas may fail silently or produce zeros. Spot-check for cells left-aligned or marked with small warning symbols, and clean up the typing format before running large formula ranges.
Losing Part Numbers During Copy-Paste
Sorting, filtering, and copy-paste operations can desynchronize part numbers from their converted dimensions. Always include the Part Number column in your sort range, and avoid manual copy-paste when a formula or lookup can be used instead.
Best Practices and RFQ Checklist
Process and Version Control
Treat the RFQ BOM like a controlled document. Add a version field, record who prepared and who approved it, and freeze a copy for each RFQ round. When a change is required, increment the version rather than silently editing a live file in email threads.
Align with Drawings and Tolerances
The BOM should never contradict the drawings. For critical parts, confirm that metric dimensions in the BOM match what you have after converting drawing dimensions and tolerances. Use the machining allowance and tolerance conversion guides when necessary to keep process plans consistent.
Communicate Expectations Early
Include a short RFQ note to suppliers explaining that the design is originally in inches, that the BOM shows both inch and mm values, and that metric values should be used for manufacturing. Invite questions before quoting to avoid surprises after order placement.
Quick RFQ Checklist
- • Imperial and metric columns available for all critical dimensions
- • Material and finish clearly mapped to local equivalents
- • RFQ quantity per line explicitly defined
- • Drawings and models referenced by controlled IDs
- • Rounding rules and units documented in the header
Related Tools
Use these tools alongside your BOM conversion workflow
BOM Batch Converter
Upload Excel or CSV BOMs, detect dimension columns, and convert inch-based values to millimeters while preserving the original table structure.
Open Tool →Machining Allowance Calculator
Plan roughing and finishing allowances in mm so RFQ dimensions align with real machining capability on the shop floor.
Open Tool →Tolerance Converter
Convert ANSI tolerance specs to ISO 286 fits before you commit them to BOM and RFQ data for metric suppliers.
Open Tool →Send Clean RFQs to Global Suppliers
Use this guide as a checklist, convert your BOM with the batch tool, and keep both imperial and metric data aligned. A well-structured RFQ BOM saves time for you and your suppliers, and makes cost comparisons much more reliable.