What this calculator does
The calculator rearranges the exponential survival relationship: MTBF = −t ÷ ln(R). It links a mission requirement to a rate-based reliability target.
When to use it
Use it during early requirements, vendor discussions, or test planning when constant failure intensity is an accepted engineering assumption.
Inputs and formula
Enter target mission reliability as a decimal and mission time in hours. A target of exactly one cannot be converted to a finite MTBF.
Worked example and interpretation
To reach 90% reliability for a 100-hour mission, required MTBF is about 949 hours. That requirement applies only to the stated mission and model.
Practical notes and limitations
MTBF is not a universal quality score. If reliability changes with age, use a Weibull fit instead. See MTBF, MTTF, and MTTR explained before publishing requirements.