Data source & methodology
- Definitions: ITU-T recommendation G.1010 and Y.1541 provide targets for one-way delay, jitter, and loss for IP services.
- Consumer guidance: U.S. FCC “Household Broadband Guide” outlines indicative bandwidth needs for common activities.
- Throughput model: Effective throughput ≈ nominal rate × (1 − overhead) × (1 − loss). Latency indirectly constrains single-stream TCP; this tool assumes modern congestion control and typical browser transfer behavior.
All calculations strictly follow the formulas and data outlined in these sources.
Direct references: ITU-T G.1010, ITU-T Y.1541, FCC Household Broadband Guide.
The formula explained
Unit conversions:
\\[ 1~\\text{byte} = 8~\\text{bits},\\quad 1~\\text{Mbps} = 10^6~\\text{bits/s} \\]
Effective throughput (fractional model):
\\[ T_{\\mathrm{eff}} = T_{\\mathrm{nominal}} \\times (1 - o) \\times (1 - l) \\]
where \\(o\\) is protocol/medium overhead (0–0.5), \\(l\\) is packet loss fraction (e.g., 0.01 for 1%).
Download/Upload time for a file of size \\(S\\) bytes:
\\[ t = \\frac{S \\times 8}{T_{\\mathrm{eff}}} \\]
Concurrency for an activity requiring \\(R\\) (bits/s):
\\[ N \\approx \\frac{T_{\\mathrm{eff}}}{R \\times (1 + m)} \\] with margin \\(m\\) (default 0.25) for variability.
Glossary of variables
| Symbol / Field | Meaning |
|---|---|
| Download speed | Advertised downstream line rate. |
| Upload speed | Advertised upstream line rate. |
| Overhead (o) | Protocol/Wi-Fi/VPN overhead fraction (e.g., 0.07 = 7%). |
| Loss (l) | Packet loss fraction (e.g., 0.01 = 1%). |
| Latency | Round-trip time (ms). Affects interactive responsiveness and can limit single-stream TCP. |
| Jitter | Variation in latency (ms), important for real-time media. |
| File size (S) | Size of the object to transfer (KB/MB/GB/TB). |
| Teff | Effective throughput after overhead and loss. |
How it works: a step-by-step example
Scenario: 100 Mbps down / 20 Mbps up, overhead 7%, loss 0.5%, file = 1.5 GB.
- Convert 100 Mbps to bits/s: \\(100\\times10^6\\).
- Compute effective down: \\(T_{eff} = 100\\,\\text{Mbps} \\times (1-0.07) \\times (1-0.005) \\approx 92.6\\,\\text{Mbps}\\).
- File bits: \\(1.5\\,\\text{GB} = 1.5\\times10^9\\,\\text{bytes} = 12\\times10^9\\,\\text{bits}\\).
- Time: \\(t = 12\\times10^9 / 92.6\\times10^6 \\approx 129.6\\,\\text{s} \\approx 2\\,\\text{min}~10\\,\\text{s}\\).
Frequently asked questions
How do overhead and loss change results?
They reduce usable throughput. Even a fast line may deliver less net payload due to headers, acknowledgements, retransmissions, Wi-Fi retries and VPN encapsulation.
What numbers should I trust: ISP portal, router, or Speedtest?
Use multiple sources. ISP portals measure line sync; router stats include LAN factors; browser speed tests reflect end-to-end app performance.
Does Wi-Fi vs Ethernet matter?
Yes. Wi-Fi adds contention, airtime overhead and interference. Ethernet delivers lower latency, loss and jitter, improving effective throughput.
How much headroom should I keep?
Reserve 20–30% for variability, especially with multiple devices and real-time apps.
Can I boost single-stream download speeds?
Use wired connections, modern browsers, updated OS/TCP stacks, and prefer servers/CDNs closer to you. Parallel connections (where safe/legal) can also help.
Tool developed by Ugo Candido. Content verified by the CalcDomain Editorial Board.
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