Bandwidth, Latency and Throughput

Kite Studio pays for a "100 megabit" fibre line. Yet a video call with a client in Toronto stutters while a big upload runs, and the upload itself is slower than the sales brochure promised. Three different words describe three different problems here, and mixing them up leads to buying the wrong fix.

The rule

Bandwidth is the pipe's width, latency its length, throughput what actually flows.

Bandwidth is the maximum rate a link can carry, measured in bits per second: Kite Studio's line is 100 Mbps (megabits per second). It is a capacity, like the width of a pipe.

Latency is the time one piece of data takes to get from one end to the other, measured in milliseconds (ms). It depends mainly on distance and on how many devices the data passes through. Engineers often quote the round-trip time (RTT): there and back again. From India to Toronto the round trip is well over 150 ms however wide the pipe is, because light in fibre can only go so fast and the path is long.

Throughput is the rate you actually achieve, also in bits per second. It is always at most the bandwidth, and usually lower because of other traffic sharing the link, protocol overhead, lost packets being resent, or a slow server on the far end.

Watch the units: network speeds are in bits (small b, Mbps); file sizes are usually in bytes (capital B, MB). One byte is 8 bits.

The shortcut

For any "how long will it take?" question, convert to bits first, then divide by the rate: time = (size in bytes × 8) ÷ rate in bits per second. And for any "it feels slow" complaint, ask: is it a lot of data (bandwidth/throughput) or a lot of back-and-forth (latency)?

The trap is the forgotten × 8: reading "100" on the line and "50" on the file and guessing half a second.

Drills

Answer fast — trust the rule.

Best-case seconds to send a 50 MB file over the 100 Mbps line:

Seconds to send a 200 MB archive at a measured 80 Mbps:

Remember

• Bandwidth is the pipe's width, latency its length, throughput what actually flows.
• Time = bytes × 8 ÷ bits per second — convert before you divide.
• More bandwidth does not cut latency; many small round trips feel slow on any pipe.