Authoritative data source & methodology

Primary references:

  • IETF RFC 6349 — Framework for TCP Throughput Testing (2011). Provides practical methodology for measuring TCP efficiency and overhead.
  • IEEE 802.3 — Ethernet framing overhead specifications (various clauses) impacting payload efficiency.
  • FCC Broadband Speed Guide — typical consumer broadband rates and considerations for real-world throughput.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The formula explained

$$ t = \frac{S}{R_{\mathrm{eff}}} \quad \text{where} \quad R_{\mathrm{eff}} = \bigl(\min(R_{\mathrm{line}},\, R_{\mathrm{cap}}\times N)\bigr)\times (1 - \mathrm{OH}) $$

\(S\) = file size (bits), \(R_{\mathrm{line}}\) = nominal line rate (bits/s), \(R_{\mathrm{cap}}\) = server per-connection cap (bits/s, optional), \(N\) = parallel streams, \(\mathrm{OH}\) = overhead fraction (e.g., 0.10 for 10%), \(t\) = time (seconds).

Glossary of variables

Symbol / Field Meaning Units
File size (S)Total content to transferB, KB, MB, GB, TB
Line speed (Rline)Nominal link rateKbps, Mbps, Gbps
Overhead (OH)Protocol + framing + loss allowancePercent (%)
Per-connection cap (Rcap)Server limit for one TCP/HTTP stream (optional)Kbps, Mbps, Gbps
Parallel streams (N)Concurrent connections used to fetchcount
Effective throughput (Reff)Achievable data rate after constraintsbps
Time (t)Estimated completion timeseconds

How it works: a step-by-step example

Example

Inputs: 3 GB file, line speed 100 Mbps, overhead 10%, no server cap, 1 stream.

  1. Convert size: \(3\,\mathrm{GB} \approx 3 \times 1024^3 \times 8 = 25{,}769{,}803{,}776\) bits.
  2. Effective throughput: \(R_{\mathrm{eff}} = 100\,\mathrm{Mbps} \times (1 - 0.10) = 90\,\mathrm{Mbps}\).
  3. Time: \(t = S/R_{\mathrm{eff}} \approx 25.77\times 10^9 / 90\times 10^6 \approx 286.3\,\mathrm{s} \approx 4:46\).

FAQ

Is the calculator using decimal (MB=1,000,000 bytes) or binary (MiB) units?

Inputs accept common decimal units (KB, MB, GB, TB) converted as 1 KB = 1,000 bytes by default for user familiarity. Results display throughput in both bits/s and bytes/s for clarity.

What if the per-connection cap is unknown?

Leave it blank; the model will assume only your own line speed and overhead determine the effective rate.

Why does measured speed differ from my plan speed?

ISPs advertise maximums; real conditions (Wi-Fi quality, congestion, routing) reduce throughput. Adjust overhead until the effective throughput matches a recent speed test for best predictions.

Does splitting a file into multiple parts help?

It can if the server limits per-connection speed. Set a per-connection cap and raise streams to see the expected benefit—capped at your line speed.

How do I convert Mbps to MB/s quickly?

Divide by 8 (e.g., 80 Mbps ≈ 10 MB/s). The results panel shows both for convenience.

Tool developed by Ugo Candido. Content reviewed by CalcDomain Editorial Board.
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