Bandwidth Calculator
Solve size ÷ speed = time in any direction. File sizes use binary KB/MB/GB/TB (1024). Link speeds use decimal Kbps/Mbps/Gbps — the tool applies the ×8 bits-per-byte conversion automatically.
Solve for
Transfer time
8.39 s
~11.92 MiB/s at this link rate (ideal). Real downloads are often 5–15% slower.
How to use
- Choose Solve for: transfer time, file size, or required speed.
- Enter the two known values (e.g. 100 MB file + 100 Mbps link when solving time).
- Pick units: binary KB/MB/GB/TB for files; decimal Kbps/Mbps/Gbps for link speed.
- Use speed presets (25–10000 Mbps) for common fiber and LAN links.
- Read the large result — add ~15% for HTTPS overhead on real downloads.
- Click Copy results for estimates in tickets or planning docs.
FAQ
Why does 100 MB take 8 seconds on 100 Mbps?
MB is megabytes; Mbps is megabits per second. 100 MB = 800 megabits. 800 ÷ 100 Mbps = 8 seconds at 100% efficiency. This is the most common 'slow Internet' misunderstanding.
Why is my real download slower than the calculator?
The tool assumes 100% line use. TCP/IP, TLS, and congestion often cost 5–15% on good links; VPN or Wi‑Fi can add much more. Multiply ideal time by ~1.15 for rough HTTPS planning.
KB vs KiB — which does this use?
Binary sizes: 1 KB = 1024 bytes (Windows file properties). Link speeds use decimal Mbps (1 Mbps = 1,000,000 bits/s) like ISPs quote.
Can I find how fast a link must be for a deadline?
Yes. Choose **Required speed**, enter file size and target time in seconds — the tool solves minimum Mbps/Gbps.
Does this measure my actual Internet speed?
No. It is math only. Use a speed test site to measure live throughput; use this calculator to plan transfers from size + rated speed.
Does data leave my browser?
No. All math runs locally.
Introduction
Bandwidth Calculator rearranges one equation three ways:
time = (file size in bytes × 8) / speed in bits per second
Enter any two of file size, link speed, and transfer time — get the third. It automatically handles megabytes vs megabits and unit toggles for everyday planning (game downloads, backups, uploads).
How the calculator works
Units
| Type | Units | Convention |
|---|---|---|
| File size | KB, MB, GB, TB | Binary (1024-based), like Windows |
| Link speed | Kbps, Mbps, Gbps | Decimal (1000-based), like ISP ratings |
Solve modes
| Mode | You enter | Result |
|---|---|---|
| Transfer time | File size + speed | Seconds / minutes |
| File size | Time + speed | Max data in chosen size unit |
| Required speed | File size + time | Minimum link rate |
Speed presets
One-click: 25, 100, 300 Mbps fiber, 1 Gbps, 2.5 GbE, 10 GbE — fills the speed field when solving time or size.
Throughput helper
When solving time, the tool also shows approximate MiB/s at the line rate (speed_bps ÷ 8 ÷ 1024²) for intuition (e.g. 100 Mbps ≈ 11.9 MiB/s).
Understanding results
Ideal vs real world
| Scenario | Planning factor |
|---|---|
| LAN gigabit, large sequential file | Often 95%+ of ideal |
| HTTPS download from Internet | Often ×1.10–1.15 ideal time |
| VPN / high latency | ×1.3–1.5 or more |
| Congested Wi‑Fi / cellular | ×2+ possible |
Quick reference (100% efficiency)
| Link | ~MiB/s | 4 GiB file |
|---|---|---|
| 25 Mbps | ~3 | ~22 min |
| 100 Mbps | ~12 | ~5.5 min |
| 300 Mbps | ~37 | ~1.8 min |
| 1 Gbps | ~119 | ~33 s |
What this measures
| Measured | How |
|---|---|
| Theoretical transfer time | Size × 8 / bps |
| Required bitrate for a deadline | Size × 8 / seconds |
| Max transferable size in a window | bps × seconds / 8 |
What this does NOT measure
| Not measured | Why |
|---|---|
| Live speed test | No network probe |
| Packet loss / latency | Not in formula |
| Disk read/write speed | Bottleneck may be storage |
| Parallel streams / CDN | Single-stream ideal |
| Compression | Uses raw file size you enter |
Safety
Calculator only — no network traffic generated.
Common use cases
Game or ISO download estimate
100 GB at 300 Mbps → ideal ~44 min; plan ~50 min with overhead.
Upload deadline
Need to push 50 GB in 2 hours? Solve required speed → minimum Mbps.
Explain MB vs Mbps to someone
100 MB on 100 Mbps = 8 s — calculator shows the math instantly.
Related tools
- RAM Latency Calculator — DRAM CAS timings, not network throughput.
- Byte Calculator — convert storage units without time math.
- Memory Test — browser tab heap, unrelated to link speed.
- WebRTC Leak Test — IP exposure through WebRTC, not bandwidth planning.