How this calculator works
- Step 1Turn the size into bits40,00,00,00,0005 GB × 1,000,000,000 bytes × 8 bits.
- Step 2Take off overhead100.00 MbpsPart of the speed carries protocol data, not your file.
- Step 3Divide6 min 40 sBits ÷ useful bits a second.
File sizes are counted in bytes, but connection speeds in bits. One byte is eight bits, which is the most common source of confusion.
Worked example: a 5 GB download
5 GB on a 100 Mbps connection takes at least 6 min 40 s.
- Time
size in bits ÷ useful speed in bits a second
- Size in bits40,00,00,00,000
- Speed in bits a second10,00,00,000
- Seconds400
- With 10% overhead7 min 24 s
- Time6 min 40 s
Reading the result
- 5 GB6 min 40 sGigabytes of 10⁹ bytes, as storage makers and websites use.
- 5 GiB7 min 9 sGibibytes of 2³⁰ bytes, which Windows labels as GB.
- b and BSmall b is bits; capital B is bytes, eight times larger.
- MbpsThe unit internet plans are sold in.
- MB/sThe unit download managers often show.
- Real speeds varyWi-Fi, distance and busy servers make transfers slower.
Related developer tools
Transfer time depends on size and speed, and on whether units are decimal or binary.
To plan an IPv4 network, use the IP subnet calculator. For bit-level arithmetic, try the binary calculator.
Common mistakes
Mistake: Expecting 100 Mbps to download 100 MB a second.
Instead: Divide by 8: 100 Mbps is at most 12.5 MB/s.
Mistake: Mixing up GB and GiB for large files.
Instead: Check which unit your system shows; the gap is about 7%.
Mistake: Planning backups on the plan speed alone.
Instead: Add an overhead allowance and test the real upload speed.
Read how we test our calculators, or browse more developer tools.