Split CDN load across points of presence and check the origin request rate and egress that survives the cache hit ratio.
Anycast routing spreads requests roughly evenly across points of presence, and everything the edge can answer never reaches the origin. The miss fraction is what determines origin sizing, and because it multiplies the full object size it dominates origin egress cost. Cache hit ratio has brutal leverage on origin load: dropping from 95% to 90% doubles the requests hitting your origin, which is why cache-key and TTL design is a capacity decision, not a tuning detail.
CDN Edge Distribution
requests per PoP = total ÷ PoPs; origin requests = total × (1 − cache hit ratio); egress = request rate × object size × 8.
requests per PoP = total ÷ PoPs; origin requests = total × (1 − cache hit ratio); egress = request rate × object size × 8. Anycast routing spreads requests roughly evenly across points of presence, and everything the edge can answer never reaches the origin. The miss fraction is what determines origin sizing, and because it multiplies the full object size it dominates origin egress cost.
Cache hit ratio has brutal leverage on origin load: dropping from 95% to 90% doubles the requests hitting your origin, which is why cache-key and TTL design is a capacity decision, not a tuning detail.
This calculator takes 5 inputs: Total requests per second, Points of presence, Edge cache hit ratio, Average object size, Origin capacity. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.