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Enter how many machines use the part, its MTBF, the lead time and the costs to get the lowest total cost stock, the stock for your target service level and the expected downtime from missing spares.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Probability that demand during the lead time fits within the stock. The line marks the target level.
Cost of holding the parts plus the expected cost of downtime when they are missing.
The report gathers this page's inputs, results, equations, assumptions and references, with fields for project, engineer and revision. In the print dialog, choose Save as PDF.
Compute the average demand during the replenishment lead time and use the Poisson distribution. Then compare the cost of holding each extra part with the expected downtime it avoids; the lowest total cost quantity is optimal.
Yes, if downtime is expensive and the lead time long. That is an insurance spare: even with rare use, expected downtime cost exceeds the cost of holding the part.
Major spares expected to be used over more than one period are generally capitalized as property, plant and equipment (ASC 360); routine spares are materials and supplies.
Important notice: Indus Metrics tools produce estimates and pre-sizing results from the data you enter and from published engineering methods. They do not replace design, calculations or reports signed by a licensed professional engineer (PE), nor verification against the applicable codes, standards and regulations, such as OSHA rules and the ASME codes. Material and fuel properties vary: check manufacturer data or your own process analyses before deciding. By using this site you agree to the Terms of Use.
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