Bandwidth-Delay Product Calculator
Calculate the Bandwidth-Delay Product (BDP) to determine optimal TCP window sizes and understand how much data your network can keep in transit.
Run BDP Calculator
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Bandwidth-Delay Product
In transit: 50,000 bits
In bytes: 6,250 Bytes
Recommended TCP Window: > 6.10 KB
Why this matters
The Bandwidth-Delay Product (BDP) determines the amount of data that can be in transit in the network. For a TCP connection to achieve maximum throughput, the TCP Receive Window size must be at least as large as the BDP. If the window is smaller, the sender will stall waiting for acknowledgments before the pipe is full.
Who this Lab is for
Designed for
- Network Engineers
- Systems Administrators
- DevOps Engineers
Use it when
- Tuning TCP performance for long-fat networks (LFN)
- Troubleshooting slow file transfers over high-latency links
- Designing global replication topologies
A complete run, step by step
Input Bandwidth
Enter the available link capacity and unit (e.g. 10 Gbps).
Input Latency
Enter the Round Trip Time (RTT) in milliseconds.
Review Calculation
Read the BDP output and recommended TCP window size.
Tune and Verify
Apply the recommended window size to your OS or application and verify with iperf3 or similar tool.
What you will need
Prepare the following information before starting. Use measured evidence where possible; defaults are examples and should not be treated as recommendations.
Bandwidth (Mbps)
The link bandwidth in megabits per second.
Round-Trip Time (ms)
The network round-trip latency in milliseconds.
What the result tells you
Your report includes
- Determine the exact BDP in bytes and bits
- Find the recommended TCP receive window size
- Visualize the impact of latency on throughput
How it is determined
Calculates the product of bandwidth and latency (RTT) to determine the amount of unacknowledged data that can be in flight.
Standard TCP window size calculation based on network bandwidth and RTT. BDP = bandwidth × RTT is a textbook formula with no ambiguity.
Model assumptions
- • Assumes typical TCP congestion control behavior without scaling limits unless specified.
- • Bandwidth and latency values are steady-state averages without burst or jitter.
- • Result represents a theoretical maximum; real-world window sizes may be constrained by OS or hardware limits.
Authoritative references
WAN File Transfer
Situation
A 1 Gbps link with 50ms RTT.
Result
BDP is 6.25 MB. The TCP window must be at least 6.25 MB to fully utilize the link.
Use the result with engineering judgement
- Theoretical maximum assuming no packet loss
- Does not account for application-level framing or overhead
Questions before you begin
Why is my file transfer slow on a fast connection?
If your TCP window size is smaller than the Bandwidth-Delay Product, the sender will pause to wait for acknowledgements, leaving the network pipe partially empty.
What is a long-fat network (LFN)?
A long-fat network has a high BDP — high bandwidth combined with high latency, such as a transatlantic satellite link. Standard TCP defaults are poorly tuned for LFNs and require window scaling (RFC 7323) to be enabled.
How does packet loss affect BDP tuning?
Even a small amount of packet loss (e.g. 0.1%) dramatically reduces the effective throughput on high-BDP links because TCP backs off its congestion window aggressively. Use CUBIC or BBR congestion control for better resilience.
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