Bandwidth Calculator
Four bandwidth tools in one card: convert between any data-rate or data-size unit, estimate a file’s transfer time, project monthly usage from a sustained connection speed, or size a website’s bandwidth needs from its traffic. Pick a mode to switch the inputs.
Bits, bytes, and connection speed
Network speed is measured in bits per second because data travels one bit at a time down a wire or over radio; file size is measured in bytes because that’s how storage is organized (8 bits = 1 byte). The two units look similar but differ by a factor of 8, so a “100” connection (100 Mbps) moves at most 12.5 MB per second — a mix-up that leads to a lot of confused “why is my download so slow” questions.
How it’s calculated
Transfer time = file size (bits) ÷ connection speed (bits/sec). Monthly usage from a sustained speed = speed (bits/sec) × seconds in the period ÷ 8, converted to bytes. Website bandwidth = page views × average page size × redundancy factor, divided by the period’s seconds to get an average throughput. All conversions use decimal (base-1000) unit prefixes: 1 KB = 1,000 bytes, 1 Mbit = 1,000,000 bits, matching how ISPs and browsers report speed.
Real-world transfer speed is usually lower than the theoretical number here due to protocol overhead, network congestion, and the far end’s own speed limits; treat results as a best-case ceiling.
Worked example
A 100 MB file over a 50 Mbit/s connection: 100 MB = 800 million bits, so 800,000,000 ÷ 50,000,000 = 16 seconds. A sustained 10 Mbps connection running 24/7 for 30 days moves 10,000,000 × 2,592,000 ÷ 8 = 3,240 GB (3.24 TB) in that month. A site with 100,000 monthly page views averaging 2 MB per page and a 1.5× redundancy factor needs roughly 0.93 Mbps of average bandwidth — though real traffic clusters, so provisioning several times that average is standard practice.
Common internet connection speeds
For reference: dial-up modems topped out around 56 Kbit/s; standard home broadband (ADSL2+/cable) runs 24–100 Mbit/s; fiber connections commonly offer 300 Mbit/s to 2 Gbit/s; Gigabit Ethernet moves 1 Gbit/s over a wired LAN; and 5G mobile can reach 400–3,000 Mbit/s under good conditions, though real-world speeds vary widely with congestion and distance from the nearest tower or node.
Common mistakes
- Confusing Mbps (megabits per second, a speed) with MBps or MB/s (megabytes per second, 8× larger) — always check the case of the “b.”
- Forgetting overhead: real transfers rarely hit the full theoretical line speed, especially over Wi-Fi or long distances.
- Sizing website bandwidth on human traffic alone and ignoring search-engine and AI crawlers, which can generate as much or more traffic than real visitors.
- Assuming average bandwidth is enough — traffic spikes (a viral post, a sale) can be many times the daily average.
Where it is used
- Estimating how long a backup, game download, or video export will take on a given connection.
- Choosing an internet plan based on realistic monthly data needs.
- Sizing server or CDN bandwidth for a website launch.
- Converting between the bit- and byte-based units used across networking and storage specs.
Frequently asked questions
What's the difference between bits and bytes?
A byte is 8 bits. Network speeds are almost always quoted in bits per second (Mbps, Gbps) while file sizes and storage are quoted in bytes (MB, GB) — so a 100 Mbps connection transfers at most 12.5 MB per second, not 100 MB. Mixing the two up is the single most common bandwidth math mistake.
Why is my actual download slower than my plan's advertised speed?
Advertised speed is the link’s theoretical capacity; real transfers lose some throughput to protocol overhead (TCP/IP headers), Wi-Fi conditions, and the server’s own upload speed, which is often the real bottleneck. A 100 Mbps connection typically delivers noticeably less in practice, especially from busy or distant servers.
How do I estimate bandwidth for a small website?
Multiply page views by average page size, then add a redundancy factor (typically 1.3x–2x) to cover bot traffic, retries, and traffic spikes. That gives total data transferred over the period; dividing by the number of seconds in that period gives the average bandwidth your host needs to sustain — though real traffic is uneven, so peak usage during busy hours is often several times the average.
Are these unit prefixes decimal (1000) or binary (1024)?
This calculator uses decimal prefixes (1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes), matching how ISPs advertise speeds and how operating systems report network throughput. Storage capacity is sometimes shown in binary units (1 KiB = 1,024 bytes) instead, which is why a drive can show less free space than its label suggests.
How much data does streaming or video calling use?
Standard-definition video streams around 1–3 Mbps, HD around 3–6 Mbps, and 4K around 15–25 Mbps — multiply by seconds watched and divide by 8 to get bytes. A one-hour HD video at 5 Mbps uses about 2.25 GB; the download/upload time calculator above can run that math for any file size and speed combination.