Work out how many edge locations a latency target needs, from the distance budget the speed of light allows.
Subtracting processing time from the latency target leaves a propagation budget, which converts directly into a maximum user-to-edge distance at 200,000 km/s. Because locations cover area rather than distance, mean distance falls with the square root of location count — so halving latency needs about four times the footprint, which is where the cost curve bites. This is the quantitative version of 'just add more PoPs': the squared relationship means the last 10 ms costs far more than the first 50 ms, and beyond a point buying more locations is worse value than cutting processing time or payload size.
Edge Location
distance budget = (target RTT − processing) × 200,000 ÷ (2 × route factor), and because coverage grows with area, locations needed ≈ current locations × (current distance ÷ budget)², plus spares.
distance budget = (target RTT − processing) × 200,000 ÷ (2 × route factor), and because coverage grows with area, locations needed ≈ current locations × (current distance ÷ budget)², plus spares. Subtracting processing time from the latency target leaves a propagation budget, which converts directly into a maximum user-to-edge distance at 200,000 km/s. Because locations cover area rather than distance, mean distance falls with the square root of location count — so halving latency needs about four times the footprint, which is where the cost curve bites.
This is the quantitative version of 'just add more PoPs': the squared relationship means the last 10 ms costs far more than the first 50 ms, and beyond a point buying more locations is worse value than cutting processing time or payload size.
This calculator takes 8 inputs: Locations today, Average user distance to the nearest location, Latency target, Edge processing time per request, Fibre path vs straight line, Spare locations for failure, Monthly cost per location, Traffic served. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.