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
Exact size: 6,250 bytes
Binary equivalent: 0.00596 MiB
Minimum whole-byte window: 6,250 bytes
RFC 7323 window scaling: Not required by window size
Why this matters
BDP = path bandwidth × round-trip time. The whole-byte result is a theoretical lower bound for the receive window and sender congestion window to keep that path full. Treat bandwidth as achievable TCP goodput: protocol overhead, loss, congestion control, socket limits and competing traffic can reduce real throughput.
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.
Bandwidth multiplied by RTT is deterministic, with decimal bandwidth and both decimal and binary byte output kept explicit.
Model assumptions
- • Bandwidth is expressed in decimal SI bits per second and latency is round-trip time.
- • The rounded byte value is the minimum whole-byte window capacity for the calculated in-flight quantity.
- • BDP is not a throughput guarantee or an automatically optimal socket-buffer setting.
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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