Latency by Distance Calculator
The lowest possible latency between two places from the distance and the medium — light in fibre travels at about two-thirds of its vacuum speed — and how your measured ping compares with that floor.
Nothing beats the speed of light, and in glass fibre light moves at about 200,000 km/s, so every 1,000 km of path costs at least 5 ms one way and 10 ms round trip.
How the latency by distance calculator works
Nothing beats the speed of light, and in glass fibre light moves at about 200,000 km/s, so every 1,000 km of path costs at least 5 ms one way and 10 ms round trip. Real routes are longer than the straight line and add switching delay, so a ping of 1.5–2 times the physical floor is normal; much more suggests a poor route. Geostationary satellites add a fixed 240 ms round trip from the 36,000 km climb.
Formula: one-way = distance ÷ speed in the medium; RTT = 2 × one-way
Worked examples
| Inputs | Minimum round-trip time | Note |
|---|---|---|
| 12,000 km of fibre, route factor 1.3 | 156 ms | 156 ms floor; 180 ms is 1.15× — excellent |
| London to New York, 5,570 km | 66.8 ms | 66.8 ms floor |
| A 500 km link over geostationary satellite | 481.1 ms | about 481 ms |
FAQFrequently asked questions
Why is light slower in fibre?
Glass has a refractive index of about 1.47, so light travels at c ÷ 1.47 ≈ 204,000 km/s. Hollow-core fibre is close to vacuum speed and is being deployed on latency-critical routes for exactly that reason.
What is a typical route factor?
Submarine cables and backbone fibre rarely run straight: 1.2–1.5 times the great-circle distance is common, more where cables must go round a landmass. Microwave links between trading venues run nearly straight, which is why they beat fibre.
Why is a satellite so slow?
A geostationary satellite sits 35,786 km up; the signal goes up and down twice for a round trip — about 240 ms before any terrestrial distance. Low-orbit constellations at 550 km cut that to under 10 ms.
How can I reduce latency?
Only by shortening the path or the number of hops: a closer server, a CDN edge, a more direct route or peering. Bandwidth does not help — a fatter pipe is not a shorter one.
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.