Bandwidth-Delay Product Calculator
On a fast link with high latency, throughput is limited not by bandwidth but by how much data the sender can put in flight before waiting for an acknowledgement. The bandwidth-delay product captures exactly that: bandwidth times round-trip time equals the data in flight, which is the TCP window size needed to keep the link saturated. This calculator takes a bandwidth in megabits per second and a round-trip time in milliseconds, computes the BDP in bytes and kilobytes, and flags whether the default 64 KB window without scaling is enough. It also reports the throughput a given window would achieve.
Bandwidth-delay product formula
BDP bits = bandwidth (bps) * RTT (seconds)
bandwidth bps = Mbps * 1,000,000
RTT s = ms / 1,000
BDP bytes = BDP bits / 8
BDP KB = BDP bytes / 1,000
Throughput = window bits / RTT s
The window-limited throughput is the window size in bits divided by the round-trip time. If it is below the link bandwidth, the window is the bottleneck and should be raised toward the BDP.
Network tuning context
- A window smaller than the BDP caps throughput regardless of available bandwidth.
- RFC 1323 window scaling allows TCP windows beyond the 64 KB limit of the base header, needed on high-BDP paths.
- One byte is 8 bits; bandwidth is quoted in bits per second, buffers in bytes.
- KB and Mbps use SI decimal units (10^3 and 10^6) to match network conventions.
- Long fat networks (high bandwidth and high latency) have the largest BDP and most need tuning.
Bandwidth-delay product: frequently asked questions
What is the bandwidth-delay product?
The bandwidth-delay product (BDP) is the amount of data in flight on a link at any instant: bandwidth multiplied by round-trip time. It equals the buffer or TCP window size a sender needs to keep the link fully utilised. A high-bandwidth, high-latency path (a long fat network) has a large BDP.
How do I size a TCP window from it?
Set the TCP receive window at least as large as the bandwidth-delay product. If the window is smaller than the BDP, the sender stalls waiting for acknowledgements and throughput falls below the link rate. RFC 1323 (window scaling) exists precisely to allow windows larger than 64 KB on high-BDP paths.
Why does latency limit throughput?
TCP sends a window of data then waits for acknowledgement. On a high-latency link the wait dominates, so throughput equals window size divided by round-trip time. If that is below the link bandwidth, the link is underused. Raising the window up to the BDP removes the stall.
What units does this use?
Bandwidth is entered in megabits per second and round-trip time in milliseconds, the units monitoring tools report. The calculator converts to bits and seconds, computes the product in bits, then divides by 8 to give bytes and by larger units for kilobytes. One byte is 8 bits.
What is a long fat network?
A long fat network (LFN) is a path with both high bandwidth and high latency, giving a large bandwidth-delay product. Satellite links and intercontinental fibre are common examples. They need window scaling and large buffers to reach full throughput, which is why the BDP calculation matters for tuning.
Official sources
- IETF: RFC 1323, TCP Extensions for High Performance (window scaling).
- NIST: Metric (SI) prefixes for bit and byte units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.