Network Latency Calculator
The fastest a round trip can possibly be over a given distance — the physics floor no upgrade can beat — plus the realistic figure once routing and equipment are counted.
Light travels at about 300,000 km/s in a vacuum but only about two-thirds of that through glass fibre, roughly 200,000 km/s.
How the network latency calculator works
Light travels at about 300,000 km/s in a vacuum but only about two-thirds of that through glass fibre, roughly 200,000 km/s. A round trip covers the distance twice. Real paths are also longer than the straight line — fibre follows roads, coastlines and existing ducts — so a routing factor of about 1.4 is realistic, and every router, switch and firewall on the way adds processing delay. The result is a floor: no amount of bandwidth reduces it.
Formula: RTT = 2 × distance × routing factor ÷ propagation speed + equipment delay
Worked examples
| Inputs | Realistic round trip | Note |
|---|---|---|
| London to New York (5,570 km) | 84 ms | about 84 ms — close to what you really measure |
| Within a city (20 km) | 3.3 ms | about 3 ms |
| A 17,000 km intercontinental route | 245 ms | about 245 ms — the far end of the scale |
FAQFrequently asked questions
Why can I not get lower ping to a distant server?
Because of the speed of light. A 17,000 km route is about 240 ms round trip through fibre no matter what you pay — the only fix is a server closer to you.
Why is fibre slower than the speed of light?
Light travels at about two-thirds of its vacuum speed through glass, roughly 200,000 km/s.
What is the routing factor?
Fibre follows roads, railways and seabed routes rather than straight lines, so the real path is typically 1.3–1.6 times the direct distance.
Does more bandwidth reduce latency?
No. Bandwidth is how much fits in the pipe; latency is how long the pipe is. They are independent.
What latency do I need?
Under 20 ms for competitive gaming, under 60 ms for comfortable video calls, under 150 ms for conversation to feel natural.
Where these figures come from
- IEC 80000-13 — Information science and technology (quantities and units) — the decimal (kB, MB) versus binary (KiB, MiB) prefixes used throughout
- RFC 4632 — Classless Inter-domain Routing (CIDR) — the address-plan arithmetic behind the subnet calculator
- RFC 1918 — Address Allocation for Private Internets — the private ranges the subnet calculator recognises
- NIST SP 800-63B — Digital Identity Guidelines, Authentication — length over composition rules; the basis of the password guidance here
- NIST SP 800-57 Part 1 — Recommendation for Key Management — key-strength comparisons used by the key-space calculator
- National Cyber Security Centre — password guidance — UK national guidance on password policy
Last checked: September 2026. Units follow the SI decimal convention (IEC 80000-13 defines the binary alternatives); network and security figures cite the defining standard.