What is available to build?
ATB is the number of complete units your BOM lets you build from the parts you physically have, capped by the scarcest required component. It exists to tell you whether a job can actually start before you promise a delivery date. That way shortages show up during material requirements planning instead of on the shop floor.
Key characteristics
- Bound by the limiting component: ATB equals how many whole units the scarcest part allows, so one missing part caps the run. Your bill of materials software does this math across every line.
- Based on stock on hand: the count uses parts you physically have, not future supply. This is what separates it from planning that counts scheduled receipts.
- Only as accurate as your counts: average inventory accuracy is about 91% across supply management functions, below the 95% “world-class” threshold (per the Institute for Supply Management, 2024).
- Changes in real time: the number shifts as parts are received, adjusted, or consumed.
- Harder for layered products: multi-level BOMs add sub-assemblies, which makes the calculation more involved.
Example
A craft cold-brew coffee roaster bottles cold brew by the case. The BOM for one case calls for bottles, caps, labels, and concentrate.
They have enough bottles, labels, and concentrate for 400 cases, but only enough caps for 250. The caps are the scarcest part, so ATB equals 250 cases.
This gap matters. As of Q3 2024, roughly 11% of U.S. manufacturing plants cited shortages of raw materials as a key impediment to their capacity utilization, based on U.S. Census Bureau data reported by Supply Chain Management Review.
Once ATB confirms the parts exist, you can issue a manufacture order to start the run. Software like Fishbowl can flag the cap shortfall and draft a purchase order to close it, and you can review it inside manufacturing inventory software.
Related terms
FAQ
What is the difference between available to build and available to promise? Available to build counts finished units you can produce from components on hand, while available-to-promise (ATP) counts finished units already in stock, plus scheduled supply, that you can commit to a customer.
How do you calculate available to build? For each component in the BOM, divide the quantity on hand by the amount one unit needs; the smallest result is your available to build.
Why does available to build matter? It tells you whether a job can start before you commit to a delivery date, so component shortages surface during planning instead of mid-production.