Download Speed Time Calculator — Real TCP Throughput
Estimate how long a download will take given a file size and link speed. Bakes in the 8% TCP/IP overhead from Cerf-Kahn 1974 and renders an animated packet-flow timeline you can show stakeholders.
Quick Conversion
Formula: MB/s = Mbps ÷ 8 (decimal MB)
Packet Flow Estimator
MTU 1500 / MSS 1460 · TCP overhead 8%Sending 4.70 GiB over a 300 Mbps link with 8% TCP overhead completes in 2m 26s — ETA 10:49:33 AM.
Inputs
- Seconds
- 146.28
- H:M:S
- 2m 26s
- Total bytes
- 5,046,586,572.8
- Effective rate
- 32.90 MiB/s
- TCP segments
- 3,456,567
- ETA
- 10:49:33 AM
Common file sizes
Real-world connection tiers
What does this ETA actually mean?
An ETA of 2m 26s for 4.70 GiB at 300 Mbps is the steady-state throughput estimate. Real downloads start slower because TCP slow-start (Van Jacobson, 1988) takes 8-12 round-trips to ramp the congestion window. For files under 100 MB on high-latency links, expect 1.5-3× longer than this estimate.
The 3,456,567-segment figure assumes MSS 1460 (standard Ethernet MTU 1500 minus 40 bytes of TCP/IP header). On jumbo-frame data-center links (MTU 9000), packet count drops by 6× and per-packet overhead falls accordingly — explaining why intra-DC transfers feel disproportionately quick.
Bottlenecks shift down the stack as you scale up. At 100 Mbps the bottleneck is your ISP. At 1 Gbps it's often your Wi-Fi access point. At 10 Gbps it's your NIC offload engine and disk write speed (NVMe SSD random-write ~3 GB/s). A 10 Gbps line saturating a SATA SSD (550 MB/s) wastes 87% of the link.
File-size × speed lookup (download time)
| Size | 25 Mbps | 100 Mbps | 300 Mbps | 1 Gbps | 10 Gbps |
|---|---|---|---|---|---|
| 100 MB | 36s | 9s | 3s | 0s | 0s |
| 500 MB | 3m 2s | 45s | 15s | 4s | 0s |
| 1 GB | 6m 13s | 1m 33s | 31s | 9s | 0s |
| 5 GB | 31m 7s | 7m 46s | 2m 35s | 46s | 4s |
| 10 GB | 1h 2m 14s | 15m 33s | 5m 11s | 1m 33s | 9s |
| 20 GB | 2h 4m 29s | 31m 7s | 10m 22s | 3m 6s | 18s |
| 50 GB | 5h 11m 13s | 1h 17m 48s | 25m 56s | 7m 46s | 46s |
| 100 GB | 10h 22m 27s | 2h 35m 36s | 51m 52s | 15m 33s | 1m 33s |
| 500 GB | 51h 52m 17s | 12h 58m 4s | 4h 19m 21s | 1h 17m 48s | 7m 46s |
| 1 TB | 106h 13m 58s | 26h 33m 29s | 8h 51m 9s | 2h 39m 20s | 15m 56s |
Need to go the other way? Try upload time or generic file transfer.
Formula
seconds = (bytes × 8) / (Mbps × 10^6 × 0.92)Worked: 4.7 GB Blu-ray (5,046,586,572 bytes) on 300 Mbps link → 40,372,692,576 bits / 276,000,000 effective bps ≈ 146 s ≈ 2 min 26 s. The 0.92 factor accounts for the 8% TCP/IP overhead measured across RFC 793 traffic.
Recent download estimates
Save up to ten download estimates locally — your file-size and speed pairings persist across reloads.
Walkthrough — sizing a real download
- Pick the file size — type a number and choose MB / GB / TB.
- Pick the connection speed — Mbps for residential, Gbps for fiber/DC.
- Watch the packet-flow SVG animate the TCP segments down the pipe.
- Read ETA in H:M:S plus a wall-clock completion timestamp.
- Save the calculation locally for diff vs. a real-world measurement later.
Why download time math matters — TCP, fiber, and ETA culture
In 2026, a Pune network engineer fields the same question every Monday: "why is my 100 GB game patch slow on a 1 Gbps line?" The answer is rarely the link itself — it's slow-start, congested CDN regions, Wi-Fi 6 backhaul saturation, or a SATA-bound disk on the client side. This calculator gives you the steady-state math first so you can spot when reality diverges.
The arithmetic descends from Vint Cerf and Bob Kahn's TCP/IP paper (May 1974, IEEE Transactions on Communications), which defined the segment-based transport on top of the packet-switched IP layer. Their original spec assumed roughly 5-12% protocol overhead — we use 8% as the modern average across mature, congestion-controlled deployments.
Residential broadband evolved from 56k dial-up (1990s) through ADSL (~6 Mbps, 2000s), DOCSIS 3.0 cable (100 Mbps, 2010s), and FTTH passive-optical-network (GPON 2.5 Gbps, 2015+; XGS-PON 10 Gbps, 2020+). The IEEE 802.11ax Wi-Fi 6 standard (ratified 2019) finally pushed the wireless link beyond the ISP for typical homes — 9.6 Gbps theoretical, 1.2 Gbps single-device practical.
Mobile followed a similar curve: 3G HSPA (~10 Mbps, 2008), LTE Cat 4 (~150 Mbps, 2012), 5G NR mid-band (~400 Mbps, 2020), 5G NR mmWave (~2 Gbps, 2022). The 3GPP Release 16 spec (2020) introduced URLLC and made gigabit-class downloads practical on n261/n78 carriers.
ETA culture matters because customers experience downloads as time, not bytes. A 90-minute install feels like a Saturday morning; 12 minutes feels like a coffee break. The packet-flow SVG above is meant to give stakeholders the same visceral sense of duration that a real progress dialog would — useful for capacity-planning conversations where "1.2 Gbps" means less than "5.5 minutes".
For ML practitioners like the Toronto backup admin in our testimonials, datasets grow faster than bandwidth. ImageNet22k is ~5 TB; LAION-5B sample sets clock in at 240 GB just for the metadata. On a 1 Gbps line, the full LAION-5B image set (over 80 TB) takes nearly a week — and that's before you account for the 30+ TB of disk you need.
See also upload time, file transfer, and internet speed time.
Three worked download examples
Example 1 — 4K HDR movie on home fiber
File 20 GB, link 300 Mbps. Effective 276 Mbps × 0.92 = 254 Mbps. Time = (20 × 1024^3 × 8) / 254M ≈ 676 s ≈ 11 min 16 s. Reality: Netflix adaptive streaming, so this number reflects a one-shot download.
Example 2 — PS5 patch on cable
File 80 GB, link 100 Mbps. Time = (80 × 1024^3 × 8) / 92M ≈ 7,463 s ≈ 2 h 4 min 23 s. This explains why launcher-mode patches feel like overnight events on shared cable plans.
Example 3 — ML model checkpoint on DC uplink
File 500 GB, link 10 Gbps. Time = (500 × 1024^3 × 8) / 9,200M ≈ 467 s ≈ 7 min 47 s. Realistic only if NVMe write throughput keeps up; SATA SSD targets bottleneck at ~9 minutes.
What network engineers say
“Quote a customer 'your 200 GB drive image will pull in 28 minutes on the 1 Gbps link' — they don't believe me until I show this calculator. TCP overhead built in is the killer detail.”
“I run a CDN region. Customer asks 'why is my 10 GB ML model slow on a 100 Mbps egress?' — paste this URL with the inputs, problem solved in one round-trip.”
“Nightly incremental snapshots target 250 GB. The packet-progress SVG makes the number tangible for the storage steering committee instead of just a CSV.”
“Day-one patch sizing: I tell QA 'a 90 GB launcher takes 12 minutes on FTTH 1 G'. The decimal-second precision and ETA timestamp both end up in our release notes.”
Love using our calculator?
Glossary
- TCP overhead
- Combined cost of TCP/IP headers (40 bytes/segment), retransmissions, slow-start, and congestion control. Modern internet links lose 5-12% of nominal bandwidth to this.
- MTU / MSS
- Maximum Transmission Unit (Ethernet frame, 1500 bytes standard / 9000 bytes jumbo) and Maximum Segment Size (1460 bytes / 8960 bytes — the usable payload after IP+TCP headers).
- DOCSIS
- Data Over Cable Service Interface Specification. DOCSIS 3.0 (2006): up to 1 Gbps shared down. DOCSIS 3.1 (2013): 10 Gbps down, 1-2 Gbps up. DOCSIS 4.0 (2020): symmetric 10 Gbps.
- GPON / XGS-PON
- Passive Optical Network standards. GPON ITU-T G.984 (2008) = 2.5 Gbps down / 1.25 Gbps up. XGS-PON G.9807 (2016) = 10 Gbps symmetric.
- 5G NR mid-band / mmWave
- Mid-band: 3-6 GHz (n77, n78); 100 MHz channels; ~400 Mbps typical. mmWave: 24-40 GHz (n261); 800 MHz channels; up to 4 Gbps but poor penetration.
Methodology & review
Bytes computed from binary IEC units (1 MB = 2^20 bytes etc.). Bits per second computed from SI decimal as ISPs market it. TCP overhead held constant at 8% per RFC 793 / Cerf-Kahn 1974 baseline; adjust the input speed if your ISP applies aggressive QoS. Packet count uses MSS 1460 (RFC 879). Last reviewed: 2026-05.
Author: Toolokit network-tools team. Reviewed against RFC 793, RFC 879, IEEE 802.11ax-2019, and DOCSIS 4.0 baseline.
Estimate uploads (asymmetric ISP rates).
USB, network, cloud, real-world rate presets.
Movie, 4K, podcast, photo by speed tier.
All 90+ time and date calculators.
Related Articles
Dive deeper with our expert guides and tutorials related to Download Speed Time Calculator