Network Bandwidth Calculator

Runs in browser New Internet & Network

Four calculations on one page: a rate in every unit (Mbps, MB/s, MiB/s and the rest, SI and IEC kept apart); the bandwidth needed to move a given amount of data in a given time, with an optional protocol-overhead estimate; the bandwidth for a number of users or streams plus headroom; and the bandwidth-delay product, the TCP window one connection needs to fill a link at a given round-trip time. Each result shows its formula with your numbers in it. It is arithmetic in your browser, not a measurement of any network.

Privacy: This tool runs entirely in your browser. Your input never leaves your device.

How do you work out bandwidth and transfer time correctly?

Line speeds are quoted in bits per second with SI prefixes (1 Mbps = 10^6 bit/s), file sizes in bytes, often with binary prefixes (1 MiB = 1,048,576 bytes), so the first step is always ×8 or ÷8 in the right units: a 100 Mbps line moves at most 12.5 MB/s. Transfer time is size × 8 ÷ rate, and the rate a transfer needs is size × 8 ÷ time, plus the header overhead on the wire (about 5–8% for TCP over Ethernet). Real transfers are slower than this arithmetic because of latency, congestion and TCP's window: one connection carries at most its window divided by the round-trip time (RFC 6349, RFC 7323).

How to use Network Bandwidth Calculator

  1. Choose the calculation: convert a rate, bandwidth needed for a transfer, bandwidth for users or streams, or the TCP window for a link.
  2. Fill in the fields that calculation uses (their help text says which): a data rate, a data size and the time available, a number of users and headroom, or a round-trip time.
  3. For a transfer, pick an overhead estimate if you want headers counted; leave it at none for the raw payload rate.
  4. Read the headline figures, check the formula with your numbers, and download the table as CSV if you need it.

Network Bandwidth Calculator features

  • Reads rates as you write them: 100 Mbps, 1.5 Gbit/s, 12.5 MB/s, 40 MiB/s, 56 kbit/s, "2 gigabits per second", with Arabic-Indic and Devanagari digits accepted
  • A conversion table of the same rate in 18 units, bits and bytes, SI (powers of 1000) and IEC (powers of 1024), each with its exact value in bit/s
  • Bandwidth needed to move a given size in a given time, with a choice of protocol-overhead estimates for TCP/IPv4 and TCP/IPv6 over Ethernet, or none
  • Bandwidth for a number of users or streams with a headroom margin, for sizing an office line, a video-call room or a streaming server
  • Bandwidth-delay product with a table of TCP window sizes from 64 KiB to 16 MiB, the most one connection can carry with each at your round-trip time, and whether that fills the link
  • Every result shows its formula and the same formula with your numbers substituted, so it can be checked by hand

Inputs and outputs

Inputs

  • Calculation: Convert a data rate, Bandwidth needed for a transfer, Bandwidth for users or streams, or TCP window for a link (bandwidth-delay product).
  • Data rate (convert, users or streams, TCP window), Users or streams and Headroom (%), Data size, Time available and its unit, Protocol overhead estimate, Round-trip time (ms).

Outputs

  • At a glance: the headline figure of the calculation (the rate in bits and bytes, the bandwidth needed, the total for the users, or the bandwidth-delay product) with its companions.
  • Formula and figures: the formula, the same formula with your numbers, and the size, time or rate it was based on.
  • The rate in every unit (CSV download), or the TCP window table with the ceiling each window size allows at your round-trip time.

Network Bandwidth Calculator example

Bandwidth to copy a 50 GB backup in two hours

Input:

Calculation: Bandwidth needed for a transfer · Data size: 50 GB · Time available: 2 hours · Protocol overhead estimate: TCP/IPv4 over Ethernet (5.3%)

Output:

Bandwidth needed: 58.5 Mbps (includes the overhead estimate: 5.3%) · In bytes per second (SI): 7.31 MB/s · Payload rate without overhead: 55.6 Mbps
Formula: R = S × 8 × (1 + o ÷ 100) ÷ t · Substituted: 50,000,000,000 × 8 × 1.053 ÷ 7,200 = 58,500,000 bit/s

How to read the Network Bandwidth Calculator results

Read "Bandwidth needed" as a floor: the line must sustain at least that rate for the whole time, on top of everything else that uses it.

If the rate in bytes per second seems eight times too small, the two figures are in different units: a download showing 11.9 MiB/s is a 100 Mbps line running at full speed.

In the TCP window table, "No" means a single connection with that window cannot fill the link at that round-trip time, whatever the line speed; transfers then need larger windows or several parallel connections.

Headroom is a margin you choose, not a measured figure: 20 to 30% is a common starting point for links that carry real-time traffic.

When to use Network Bandwidth Calculator

  • Checking whether a nightly backup or a database copy fits in its window on the line you have.
  • Sizing an office or branch line from the number of people on video calls at the same time.
  • Explaining why a 1 Gbps line downloads at about 119 MiB/s at best, in units the users see.
  • Tuning TCP buffers for a long, fast path between data centres from its round-trip time.

Troubleshooting

  • "Use a point as the decimal mark": write 1.5 Gbps, not 1,5 Gbps; a comma is read only as a thousands separator, as in 1,000 Mbps.
  • "Unknown rate unit": use bps, kbps, Mbps, Gbps, B/s, kB/s, MB/s, GB/s, KiB/s or MiB/s; mind the case, because Mb is megabits and MB megabytes.
  • The result is 8 times off what you expected: check whether the figure you compare with is in bits or bytes.
  • The time must be greater than zero, and the round-trip time is in milliseconds (40, not 0.04).

Frequently asked questions about Network Bandwidth Calculator

What is the difference between Mbps and MB/s?

Mbps is megabits per second (10^6 bits), the unit of line speeds; MB/s is megabytes per second (8 × 10^6 bits), what download windows usually show. So a 100 Mbps line moves at most 12.5 MB/s, or 11.92 MiB/s when the program counts 1,048,576-byte mebibytes. The table lists the same rate in every unit.

How much bandwidth do I need to upload a 50 GB backup overnight?

Rate = size × 8 ÷ time. 50 GB is 400,000,000,000 bits; in 8 hours (28,800 s) that is 13.9 Mbps of payload, or about 14.6 Mbps with the 5.3% TCP/IPv4 overhead estimate. Choose "Bandwidth needed for a transfer" to get this with your own figures, and plan for more, because the line is rarely free for the backup alone.

What is the bandwidth-delay product, and why does it matter?

It is the amount of data in flight on a link: rate × round-trip time. A single TCP connection can only carry its window divided by the round-trip time, so to fill a 1 Gbps path with 40 ms of round-trip time it needs a window of at least 5 MB. Without window scaling (RFC 7323) the window is capped at 64 KiB, which limits that connection to about 13 Mbps.

Why is the overhead only an estimate?

The extra bytes on the wire depend on the packets: the presets assume full-size 1500-byte Ethernet frames with TCP/IP headers, which is close for bulk transfers. TLS, VPN tunnels, small packets, Wi-Fi and retransmissions add more, by amounts that differ from network to network. To know what your own link delivers, measure it with a speed test.

How should I size a link for video calls or streams?

Take the rate one call or stream needs from the service's published requirements, multiply by how many run at the same time and add headroom: 25 calls at 3.5 Mbps with 25% headroom need about 109 Mbps. The calculation assumes they all peak together, which is the safe case; real peaks are usually lower.

Technical notes

Units are exact and never mixed (@engines/bandwidth): k, M, G and T are powers of 1000 (1 Mbps = 10^6 bit/s, 1 kB = 1000 B); Ki, Mi, Gi and Ti are powers of 1024 (1 MiB = 1,048,576 B), the IEC binary prefixes; a lower-case b is a bit and an upper-case B a byte of 8 bits. A comma is accepted only as a thousands separator: 1,5 is refused rather than read as 15.

Bandwidth needed is R = S × 8 × (1 + o ÷ 100) ÷ t, where o is the overhead as extra bytes per payload byte. The presets are the header cost of full 1500-byte Ethernet frames: 38 bytes of Ethernet framing (preamble, header, FCS and inter-frame gap) plus 40 bytes of IPv4 and TCP headers per 1460 bytes of data is 5.3%; TCP timestamps (12 bytes) make it 6.2%, and IPv6 headers with timestamps 7.7%.

The bandwidth-delay product is R × RTT: the bits in flight on the path. One TCP connection carries at most window ÷ RTT (RFC 6349), and without the window scale option of RFC 7323 the window cannot exceed 65,535 bytes (just under 64 KiB), so long fast paths need scaling and large socket buffers to be filled by a single connection.

Limitations and methodology

It measures nothing: every figure is arithmetic on the numbers you type. To know what your connection actually delivers, use the Internet Speed Test.

Real transfers are slower than the ideal rate because of protocol overhead, latency, TCP slow start, congestion, Wi-Fi conditions and the limits of the far end; the overhead presets cover only header bytes on full-size Ethernet frames.

The users-or-streams total assumes every stream peaks at the same time; it does not model statistical sharing or quality-of-service rules.

Security and privacy

All calculations run in your browser; the figures you enter are not sent anywhere and nothing is stored.

References

  • Metric (SI) PrefixesNISTThe SI prefixes and their exact powers of ten: kilo is 10^3, mega 10^6, giga 10^9, tera 10^12 — the meaning of k, M, G and T in Mbps, Gbps and GB.
  • units(7) — decimal and binary prefixesLinux man-pages projectLists the decimal prefixes (k = 1000) beside the binary ones (Ki = 1024, Mi = 1,048,576…) and notes in passing the b = bit, B = byte convention.
  • RFC 6349: Framework for TCP Throughput TestingIETF · 2011How to measure TCP throughput on a path: why a single connection is bounded by its window and the round-trip time (the bandwidth-delay product), and which metrics describe a test fairly.