Bandwidth Calculator
Calculate required or available network bandwidth from data size and time.
About Bandwidth Calculator
Network link speeds are quoted in bits per second (bps), but file sizes are quoted in bytes — and the two are not the same unit. The fundamental conversion is 1 byte = 8 bits. Additionally, there are two size systems: SI (decimal, 1 MB = 1,000,000 B, used by hard drives and ISPs) and IEC (binary, 1 MiB = 1,048,576 B, used by operating systems). This calculator handles both, applies an optional protocol-overhead deduction for TCP/IP headers and retransmissions, then computes the raw transfer time and a theoretical monthly capacity at full utilisation.
Formulas
Transfer time
Transfer time (s) = File size (bytes) × 8 ÷ (Link speed (bps) × (1 − overhead%))
- S_bytes
- File size in bytes
- R_bps
- Link speed in bits per second
- o
- Protocol overhead percentage (0–100)
Monthly throughput at full utilisation
Monthly bytes = Effective bps × 2,592,000 ÷ 8
- 2592000
- Seconds in a 30-day month
- R_bps
- Effective bits per second
Worked example
With the default values below, Bandwidth Calculator returns Transfer Time of 1m 24s. Change any input above and every figure here is recalculated in your browser.
Inputs used
- File / Data Sizeminimum 0
- 1,000
- Size Unitone of B (bytes), KB (1,000 B), MB (1,000,000 B), GB (1,000,000,000 B), TB (1,000,000,000,000 B), KiB (1,024 B), MiB (1,048,576 B), GiB (1,073,741,824 B), TiB
- MB (1,000,000 B)
- Link Speedminimum 0
- 100
- Speed Unitone of bps (bits/s), Kbps (kilobits/s), Mbps (megabits/s), Gbps (gigabits/s), KBps (kilobytes/s), MBps (megabytes/s), GBps (gigabytes/s)
- Mbps (megabits/s)
- Protocol Overhead (%)accepts 0–50
- 5
Results
- Transfer TimeTime to transfer the file at the given link speed.
- 1m 24s
- Transfer Time (seconds)
- 84.211
- File Size (bytes)
- 1,000,000,000
- File Size (bits)
- 8,000,000,000
- Effective Speed (bps)After applying the protocol overhead deduction.
- 95,000,000
- Monthly Capacity (GiB, full utilisation)Theoretical maximum data at 24/7 full-speed operation.
- 28,666.11
Step by step
- 1Convert file size to bytes= 953.67 MiB
- 2Convert bytes to bits (1 byte = 8 bits)= 8,000,000,000 bits
- 3Convert link speed to bits per second= 95 Mbps
- 4Apply 5% protocol overhead= 95 Mbps
- 5Transfer time = bits ÷ effective speed= 1m 24s
- 6Monthly capacity at full utilisation (30 × 24 × 3600 s)= 27.99 TiBAssumes the link is at full capacity continuously — a theoretical ceiling.
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why does my download take longer than this calculator predicts?
ISPs advertise speeds in megabits per second (Mbps), not megabytes. Your 100 Mbps connection transfers a maximum of 12.5 MB/s (100 ÷ 8). Beyond that, protocol overhead (TCP headers, retransmissions), server throttling, shared contention and Wi-Fi half-duplex losses all reduce real throughput. The overhead field lets you model a realistic figure.
What is the difference between MB and MiB?
MB (megabyte) follows the SI decimal standard: 1 MB = 1,000,000 bytes. MiB (mebibyte) follows the IEC binary standard: 1 MiB = 1,048,576 bytes. Hard drives and ISPs use decimal; operating systems typically use binary. A 500 GB hard drive is about 465 GiB as reported by Windows.
Why is '1 byte = 8 bits' important?
Because almost all consumer speed benchmarks (Speedtest, ISP plans) display megabits, but file sizes are in megabytes. Forgetting the factor of 8 is the single most common mistake when estimating download times.
What does the protocol overhead field represent?
TCP/IP adds header bytes to every packet (typically 40–60 bytes per 1,460-byte payload), and retransmissions add extra cost on lossy links. A 5–10% overhead is realistic for most Internet traffic; 0% gives the theoretical maximum the wire can carry.