BOM Explosion Calculator
Turn a multi-level bill of materials and build plan into time-phased material requirements. Free, browser-only, with CSV export.
Bill of materials and build plan
Paste comma- or semicolon-separated CSV, including the header. Use decimal points without thousands separators, YYYY-MM-DD dates, and one consistent unit per item. Use the shown column names; unrecognized columns are refused. IDs are case-sensitive text: leading zeros are kept. Each paste supports up to 5,000 data rows. Calculations run in your browser; nothing is uploaded.
parent, component, quantity_per; optional scrap_percent (20 means 20%).
parent, quantity, due_date. Parent must have a BOM definition.
item, on_hand, lead_time_days. Leave this box empty to use zeros.
Results update as you edit. On hand is used once, in due-date order. Only net shortages create component demand. Missing stock and lead times default to zero.
Requirements by level
4 item/date requirements. Quantities stay fractional; release dates use whole calendar days.
| Item | Level | Needed by | Gross | Stock used | Net | Planned release |
|---|---|---|---|---|---|---|
| KIT | 0 | 2026-11-10 | 10 | 0 | 10 | 2026-11-10 |
| BOLT | 1 | 2026-11-10 | 50 | 20 | 30 | 2026-11-09 |
| SUB | 1 | 2026-11-10 | 20 | 5 | 15 | 2026-11-08 |
| SCREW | 2 | 2026-11-08 | 60 | 10 | 50 | 2026-11-05 |
Formulas and worked example
For each component, gross requirements = parent net build × quantity per ÷ (1 − scrap % ÷ 100). Net requirements = max(0, gross requirements − remaining on hand). The component is needed at its parent’s release date. Planned release = needed-by date − lead time rounded up to calendar days.
Build 10 KITs due November 10, 2026. Each needs 2 SUBs and 4 BOLTs with 20% bolt scrap. Each SUB needs 4 SCREWs. Stock is 5 SUBs, 20 BOLTs and 10 SCREWs.
SUB gross = 10 × 2 = 20; net = 20 − 5 = 15. With a 2-day lead time, release SUBs on November 8. BOLT gross = 10 × 4 ÷ 0.8 = 50; net = 50 − 20 = 30, released November 9 with a 1-day lead time. SCREW gross = 15 × 4 = 60; net = 60 − 10 = 50. Needed November 8, release SCREWs on November 5 with a 3-day lead time.
The editable example above and these numbers are checked together in the calculation tests. This is a material plan; confirm capacity, supplier calendars and order constraints before execution.
FAQ
How are scrap and on hand applied?
Scrap is yield loss: quantity per is divided by (1 − scrap % ÷ 100). Stock is consumed once per item, earliest due date first. Only net shortages are exploded into lower-level components, including when stock covers a finished item or subassembly.
What do the levels and dates mean?
Level 0 is the finished-item requirement. A shared component uses its deepest BOM level. A component is needed on its parent's planned release date; its own release is that date minus its lead time, rounded up to whole calendar days. Missing lead times default to zero. Weekends and holidays are included.
What input is refused?
Cycles anywhere in the BOM, build parents with no BOM definition, negative quantities, scrap of 100% or more, duplicate parent/component relationships, duplicate stock totals and malformed CSV are refused. Item IDs match exactly, including case and leading zeros.
Does this include purchase orders or lot sizing?
No. This is a lot-for-lot requirements plan using the supplied on-hand stock. It does not model scheduled receipts, capacity, minimum order quantities or pack sizes. Build quantities mean required finished items; finished-item stock may cover them.
Is my data uploaded?
No. Calculations and CSV parsing run in your browser, and the numbers and files you enter are never sent to a server, unless you choose to share a link, which carries the single-item inputs in its address. The page has no ads, sign-up or third-party trackers; the site host keeps standard anonymous visit counts.
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