How this calculator works
Enter requests per second per instance, peak requests per second, capacity headroom (%), target availability (%). CalcStack applies the displayed formula and reports each intermediate planning value with the units shown.
Formula / method
Instances = ceil(peak RPS × (1 + headroom) ÷ RPS per instance)
Worked example
1,200 peak RPS, 80 RPS per instance and 30% headroom requires 20 instances.
Assumptions and limitations
Instances are homogeneous and can sustain the entered request rate.
Autoscaling delay, uneven traffic, dependencies, zones, CPU/memory limits and failover capacity require separate analysis.