Cable Latency Estimator

Estimate network latency for submarine cables, fiber optic links, and satellite connections. Enter distance to see theoretical and real-world round-trip times.

Preset Routes

How to Use

  1. 1
    Enter distance

    Type the cable distance in kilometers between two endpoints, or select a preset route like NYC to London (5,600 km).

  2. 2
    Choose cable type

    Select the transmission medium: fiber optic (submarine or terrestrial), copper, or satellite (GEO orbit).

  3. 3
    Read the results

    View theoretical one-way delay, round-trip time (RTT), and a real-world estimate that includes routing and protocol overhead.

About

The global submarine cable network spans over 1.4 million kilometers of fiber optic cable laid across ocean floors, carrying more than 95% of intercontinental data traffic. These cables are typically 17-21 mm in diameter and contain multiple fiber pairs, each capable of carrying terabits per second using wavelength-division multiplexing.

Latency in fiber optic cables is fundamentally limited by the speed of light in glass. The refractive index of the silica core (approximately 1.47) slows light to about 200,000 km/s, compared to 299,792 km/s in vacuum. This means the theoretical minimum one-way latency between New York and London (5,600 km of cable) is about 28 milliseconds.

In practice, real-world latency is higher due to signal regeneration at optical amplifiers spaced every 60-80 km, routing through network switches at landing stations, protocol overhead from TCP and TLS handshakes, and the physical cable path being longer than a straight line. These factors combine to produce round-trip times roughly 1.4 times the theoretical minimum.

FAQ

Why is fiber slower than the speed of light?
Light travels at roughly 300,000 km/s in a vacuum, but inside a glass fiber the refractive index slows it to about 200,000 km/s (approximately two-thirds of c). This is an inherent physical property of the glass core.
How does fiber compare to satellite latency?
A geostationary satellite orbits at 35,786 km altitude. A signal must travel up and back, adding about 240 ms of base round-trip time regardless of ground distance. Fiber links under 12,000 km almost always have lower latency than GEO satellite.
What adds extra latency beyond the speed of light?
Real-world latency includes optical amplifier delays every 60-80 km, routing and switching hops, TCP/TLS handshake overhead, and the fact that submarine cables follow seabed terrain rather than a straight line. These factors typically add a 1.3x to 1.5x multiplier.
Do submarine cables follow a straight-line path?
No. Submarine cables route around continental shelves, deep ocean trenches, and other cables. The actual cable length is typically 10-30% longer than the great-circle distance between landing stations.
How do CDNs reduce perceived latency?
Content Delivery Networks cache data at edge servers close to end users, so requests travel a shorter physical distance. Instead of crossing an ocean via a submarine cable, a CDN-served response may travel only a few hundred kilometers to the nearest point of presence.