What a BOM explosion is
A bill of materials, or BOM, lists the components that make one unit of a product, with the quantity of each. Some components are assemblies with BOMs of their own, so a product has several levels. A BOM explosion walks down every level and multiplies the quantities, so you know how much of each part a build needs.
ERP systems explode BOMs every time they plan. SAP's help describes MRP exploding the BOM of each assembly during the planning run to find the dependent requirements of its components. Microsoft's Dynamics 365 documentation describes the master plan turning each BOM line into a demand. This calculator runs the same explosion on a BOM you paste, without an ERP.
How to explode a BOM with this calculator
- Paste the BOM from Excel with its header row, or click Open CSV or .xlsx.
- Use either shape. A parent and component BOM has one row per relationship: parent, component and quantity per. An indented BOM has a level column, written as 1, 2 and 3, as .1 and ..2, or as 1.2.1.
- Add unit, unit cost and scrap % columns if you have them. All three are optional.
- Set the build quantity and choose the top item.
- Read the views: the indented BOM, the summarized BOM, the cost roll-up and where-used. Problems lists anything to fix.
- Click Download CSV to save the view on screen, or Copy for Excel.
The extended quantity of a line is its parent's extended quantity times the quantity per, increased by the scrap percentage. Two levels down, that is the build quantity times both quantities per, with scrap added at each level.
Get the bill of materials from the same rules as the price
Send Derik the Excel builder your team quotes from. He sends back a free map of its rules and lookup tables. If the builder also picks the components, the map shows how.
Start a conversationA worked example: a belt conveyor section
The example on this page is a 600 mm belt conveyor section, built 5 at a time. Below the top item sit a frame, two pulley assemblies, two leg stands, the belt and a gearmotor, then the parts of each assembly. The bolts are used in two places, and both pulleys use the same shell, shaft and bearing part numbers. The costs are made up to show the method. Six lines of the summarized BOM:
| Part | Description | Total for 5 | Unit cost | Extended cost |
|---|---|---|---|---|
| GM-075 | Gearmotor, 0.75 kW | 5 ea | $610.00 | $3,050.00 |
| BLT-600 | Belt, 600 mm wide | 27.3 m | $64.00 | $1,747.20 |
| PS-600 | Pulley shell, 600 mm | 10 ea | $145.00 | $1,450.00 |
| BU-30 | Bearing unit, 30 mm | 20 ea | $41.50 | $830.00 |
| ST-50 | Square tube 50 x 50 x 3 | 15.12 m | $18.40 | $278.21 |
| HW-M10 | Hex bolt M10 x 30 with nut | 122.4 ea | $0.42 | $51.41 |
The bearing unit appears twice on the pulley BOMs, two per pulley, but the build needs 20. The hex bolt appears on the frame and the leg stand. With 2% scrap the build needs 122.4, which you would round up to the box you buy. Material for one conveyor rolls up to $1,881.56, and $9,407.82 for 5.
Indented BOM, summarized BOM and where-used
- Indented BOM. Every occurrence of every part, level by level, under its parent. Wikipedia calls this a multi-level BOM shown in a parent-child, top-down form. In SAP, transaction CS12 displays a multilevel BOM, and CS11 explodes it level by level.
- Summarized BOM. Each part once, with its total quantity across all levels. SAP's summarized BOM, transaction CS13, shows each component as one item with a sum total quantity.
- Where-used. The assemblies that use a part, and every path up to the top item. SAP's where-used list is transaction CS15. Run it before you change a part, to see every product it touches.
- Cost roll-up. The material cost of each assembly, built up from its components. The BOM cost calculator adds labour and overhead to it and prices the result at your markup.
Scrap and quantity per
Scrap is material that goes into production but not into the product, such as offcuts and setup pieces. Dynamics 365 separates variable scrap, a percentage that grows with the quantity, from constant scrap, a fixed quantity lost on every production run. This calculator applies variable scrap. In the example, 5% scrap on 5.2 metres of belt asks for 5.46 metres per conveyor. Add constant scrap by hand when a setup loss matters.
Errors the explosion catches
- Cycles. A part that contains itself, directly or through other assemblies. SAP's help calls this recursiveness and notes that it is often an input error, so the explosion stops at the link and names the path.
- Missing parents. In an indented BOM, a row two levels below the row above it has lost its parent.
- A part with two costs. The same part number with a different unit cost on two rows. The roll-up uses the first and lists both.
- Quantities that are not numbers. The row is left out and named. A blank quantity counts as 1.
Bill of materials template
Download the bill of materials template for Excel, or the CSV version with the parent and component shape. The workbook holds the conveyor example twice: one sheet with parent and component rows, one as an indented BOM. Replace the rows with your own, then paste them into this page.
To make an indented BOM in Excel, start with a Level column: 0 for the finished product, 1 for its components and 2 for theirs. Each row's parent is the nearest row above it at one level up. Add the part number, description, quantity per and unit, then the unit cost and scrap if you track them. Give each part one number on every row; the part number generator helps when the scheme is new.
How AI keeps the BOM right on every configured quote
A configured product has a different BOM for every set of options a customer picks. In many plants, an Excel builder holds those rules and one or two people know how they work. A CPQ app built from that workbook configures the product and prices it line by line from the same rules. A named person approves each quote.
ThriveAI builds that app from the workbook your team quotes from, starting with a free map of its rules and lookup tables. Writing each approved configuration to the ERP as a draft item and BOM can follow the first stage. See the AI CPQ offer, and the guide to product configurator software.