Bandwidth Delay Product Calculator
Enter a link's bandwidth and round-trip latency to get the bandwidth-delay product — the data kept in flight, and the minimum TCP window you need to keep a long, fast link full.
Data in flight, instantly
Enter the bandwidth in Mbit/s and the round-trip latency in ms and the calculator returns the bandwidth-delay product (BDP) in kilobits.
Bits, not bytes
The BDP comes out in kilobits to match Mbit/s — divide by 8 to size a buffer or TCP window in kilobytes.
What is the bandwidth-delay product?
The data a link holds at once
The bandwidth-delay product is the amount of data that can be "in flight" on a network link at any instant — already sent but not yet acknowledged. This bandwidth delay product calculator multiplies two measurements, the bandwidth in megabits per second and the round-trip latency in milliseconds, to give the data volume in kilobits. Think of the link as a pipe: the bandwidth is how wide it is and the latency is how long it is, so their product is the water the pipe holds when full. That volume is exactly the buffer or TCP window you need to keep the pipe running at full speed.
Enter a bandwidth in Mbit/s and a round-trip latency in ms to get the bandwidth-delay product in kilobits instantly.
The bandwidth-delay product is simply the bandwidth multiplied by the round-trip latency.
BDP = bandwidth × round-trip latencyThe units line up neatly. A megabit per second is 10⁶ bits per second and a millisecond is 10⁻³ seconds, so Mbit/s × ms = 10³ bit = 1 kilobit. That means you can multiply the two numbers as they are and read the answer directly in kilobits — no conversion factor required. To express it as a buffer size in kilobytes, divide the kilobits by 8.
Suppose a link runs at 100 Mbit/s and a ping reports a round-trip latency of 40 ms.
Take the bandwidth and the latency
Bandwidth = 100 Mbit/s and round-trip latency = 40 ms, straight from a speed test and a ping.
Multiply them
100 × 40 = 4000 — because Mbit/s × ms gives kilobits directly.
Read the result
The bandwidth-delay product is 4000 kbit. Divide by 8 and that is 500 kilobytes — the minimum TCP window to keep this link full.
The bandwidth-delay product tells you the smallest amount of unacknowledged data that must be outstanding to keep a link fully busy. TCP works by sending a window of data and waiting for acknowledgements; if that window is smaller than the BDP, the sender runs out of data to transmit before the first acknowledgement returns, and the link sits idle. So the BDP is the minimum TCP window — and the minimum socket buffer — needed to reach full throughput. For the example above, 500 kilobytes of window keeps a 100 Mbit/s, 40 ms path saturated. The effect grows with both factors: a "long fat" link that combines high bandwidth with high latency, such as a satellite or transcontinental connection, has a very large BDP and demands large windows (enabled by TCP window scaling) to avoid throughput collapsing far below the line rate. A short, slow link has a tiny BDP and rarely needs tuning at all.
The formula is exact, but a couple of practical points are worth keeping in mind.
Mind the units and the bits-vs-bytes factor
The product is exact only when the units match: bandwidth in Mbit/s and round-trip latency in ms give the BDP directly in kilobits. The result is in bits, while buffers and TCP windows are usually configured in bytes — divide the kilobits by 8 before you size them. Use the full round-trip latency (there and back), not a one-way figure, and remember that the BDP sets the minimum window for full throughput, not a guarantee, since real throughput also depends on loss, congestion control, and middleboxes.