Latency & RTT Calculator
Turn one-way latency into round-trip time and the bandwidth-delay product, the ideal TCP window for a link of a given speed. Calculates in your browser.
Round-trip time (RTT)
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Show the math
Round-trip time is twice the one-way latency; the bandwidth-delay product is the data in flight:
RTT = 2 × latency · BDP = bandwidth × RTT ÷ 8
The bandwidth-delay product is how many bytes fill the link before the first acknowledgement returns, and the ideal TCP window size. On fast, high-latency links a small window caps throughput well below the line rate. Calculated entirely in your browser.
What this does
A latency / RTT calculator turns one-way latency into round-trip time and the bandwidth-delay product — the ideal TCP window for a link.
How to use it
- Enter the one-way latency.
- Enter the link bandwidth.
- Read RTT and the bandwidth-delay product.
How it works
The bandwidth-delay product is the data that fills a link before the first acknowledgement returns. A TCP window smaller than the BDP caps throughput.
BDP = bandwidth × RTT; RTT ≈ 2 × one-way latency
Understanding your result
The bandwidth-delay product is the key output: it is the data in flight before the first acknowledgement returns, and if your TCP window is smaller than it, throughput is capped no matter how fast the link. On long, fat links (high speed, high latency) you need a large window or parallel streams to fill the pipe, which is why a single transfer can feel slow over distance.
Example
1 Gbps with a 50 ms RTT has a bandwidth-delay product of about 6.25 MB.
Sources & methodology
Last updated .
Frequently asked questions
What is the bandwidth-delay product?
It is the amount of data that fills a link before the first acknowledgement returns, bandwidth multiplied by round-trip time. It is also the ideal TCP window size for the link.
How is RTT related to latency?
Round-trip time is roughly twice the one-way latency, since a packet must travel to the destination and an acknowledgement must come back.
Why does latency limit throughput?
On fast, high-latency links a TCP window smaller than the bandwidth-delay product caps throughput well below the line rate, because the sender must wait for acknowledgements.
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