--- title: "Download Time Calculator" date: 2026-10-14 author: "Robert A. Lee" featured_image: "https://sqmagazine.co.uk/wp-content/uploads/2026/10/download-time-calculator.jpg" --- # Download Time Calculator A 4 GB file takes **5 minutes and 56 seconds** to download at 100 Mbps when 90% of that speed reaches the file. For any file size and connection speed, the download time calculator returns this estimate and compares seven common connection types. Before it divides, it converts bytes to bits and applies a real-world efficiency allowance. Download Time Calculator Examples Reset 50 GB game at 300 Mbps 4 GB update at 100 Mbps 50 GB at 1 Gbps 700 MB on 4G (25 Mbps) File size Size unit KB MB GB TB PB MiB GiB TiB Connection speed Speed unit Kbps Mbps Gbps KB/s MB/s GB/s Share of plan speed you get % What reaches you after protocol overhead and congestion, as a share of the speed your plan advertises. Download time 24m 41s Copy A 50 GB file takes 24m 41s at 300 Mbps when you get 90% of that speed. Download time24m 41s If this size came from Windows (1,024-based)26m 31s Effective speed270 Mbps Effective speed in MB/s (what download screens show)33.75 File size in megabytes50,000 Copy all details Save scenario Share result Download CSV Saved scenarios Saved in this browser only. Each column is recalculated whenever the page loads. Time to download on common connections From 7m 24s on Fiber 1 Gbps to 12h 20m 44s on DSL 10 Mbps. This file on common connections | Connection | Time | |---|---| How this is calculated How it worksTime = size in bits ÷ (speed in bits per second × efficiency). Megabytes are decimal (1 MB = 1,000,000 bytes) unless you pick MiB, GiB or TiB, the 1,024-based units in [NIST's prefixes for binary multiples (opens in new window)](https://physics.nist.gov/cuu/Units/binary.html). Windows File Explorer counts in 1,024s but labels the result KB, MB and GB, so a size copied from it is larger than the same decimal figure (7.4% at GB), and the Windows row gives the time for that reading. Not coveredIgnores latency, slow servers and throttling; protocol overhead belongs in the efficiency you enter. Privacy**Your numbers never reach our server.** The math runs on your device, inside this page. CorrectionsReport an error in the math to [media@sqmagazine.co.uk](mailto:media@sqmagazine.co.uk?subject=Correction%3A%20Download%20Time%20Calculator); every report is reviewed and confirmed errors are corrected. Updates- Sep 28, 2026 The efficiency help text no longer claims a typical percentage; it describes the field. FeedbackHow useful was this tool? The figures shown are the worked example. Enable JavaScript to calculate with your own numbers. ## How to Use the Download Time Calculator You fill in five inputs, and the download time calculator returns four results. Because it runs in your browser, nothing you type is sent to our server. 1. Enter the size in “File size”. Then pick its unit in “Size unit”: KB, MB, GB, TB or PB for decimal sizes, or MiB, GiB or TiB for binary ones. 2. Type the speed your plan or speed test reports into “Connection speed”. Then pick “Speed unit”: Kbps, Mbps or Gbps for bit rates, or KB/s, MB/s or GB/s for byte rates. 3. Set “Real-world efficiency”, the share of that speed you expect to reach the file. Whole numbers up to 100 work, and the default is **90**. 4. Start with “Download time”, then read “Effective speed”, “Megabytes per minute” and “File size in megabytes”. 5. Tap an “Examples” chip for a preset: a 4 GB game update at 100 Mbps, 50 GB at 1 Gbps, or 700 MB on 4G at 25 Mbps. “Share result” copies a URL that reopens your inputs. Its default speed matches the Federal Communications Commission (FCC) benchmark for fixed broadband. In its [FCC Broadband Speed Benchmark](https://docs.fcc.gov/public/attachments/DOC-401205A1.txt) release, the agency set download speeds of **100 megabits per second**. Below the answer, a bar chart and a matching table run the same file through seven preset speeds. They range from DSL at 10 Mbps to fiber at 1 Gbps. However, those presets are round illustrative speeds, not measured averages for each technology. In other words, every figure in the panel comes from one division. ## How Download Time Is Calculated Download time is the file’s size in bits divided by the part of the connection speed that carries it. Sizes are counted in bytes, while speeds are counted in bits. A [NIST binary prefix reference](https://physics.nist.gov/cuu/Units/binary.html) from the National Institute of Standards and Technology lists one byte as **8 bits**. So the calculator multiplies the size by 8 before it divides. With S as the file size in bytes, R as the connection speed in bits/s and E as the efficiency setting: - Download time in seconds = (S × 8) ÷ (R × E ÷ 100). - Effective speed = R × E ÷ 100. Specifically, every unit is decimal unless you pick a binary one. NIST’s table puts one megabyte (MB) at 1,000,000 bytes and one gigabyte (GB) at 1,000,000,000 bytes. Binary units come from the International Electrotechnical Commission (IEC), which approved them in December 1998. On that scale a gibibyte (GiB) is 1,073,741,824 bytes, or 2 to the 30th power. Similarly, speeds follow the decimal rule. NIST notes that some designers of local area networks have used megabit per second to mean 1,048,576 bit/s. Even so, all telecommunications engineers use it to mean one million bits a second. The unit a size is written in changes the answer. Typed as GiB instead of GB, the same “4” carries **7.4%** more data. It takes 7.4% longer at any speed. ### Protocol Overhead: The 97.3% Ceiling Packet headers alone take about **2.7%** of every full-size packet. Fixed IPv4 and TCP headers use 40 octets of a 1,500-octet Ethernet packet. That leaves 1,460 octets, or 97.3%, for file data. Each figure comes from an Internet Engineering Task Force (IETF) specification. Under [RFC 894](https://www.rfc-editor.org/rfc/rfc894.html), the maximum length of an IP datagram sent over an Ethernet is 1500 octets. [RFC 791](https://www.rfc-editor.org/rfc/rfc791.html) counts the IPv4 header in 32-bit words and states that the minimum value for a correct header is 5, or 20 octets. [RFC 9293](https://www.rfc-editor.org/rfc/rfc9293.html) puts the fixed TCP header, in octets, at 20 in the (rare) case that no options are present. It adds that the header may be larger if TCP Options are to be sent. So 97.3% is a ceiling from two headers on one layer. Link framing, encryption, retransmissions and a busy network all come on top, and the efficiency input exists to cover them. Running the default inputs through the formula, for instance, reproduces the tool’s answer. ## Worked Example: A 4 GB File at 100 Mbps By default, the calculator opens at 4 GB and 100 Mbps, with efficiency set to 90. Four steps rebuild its panel: 1. Size in bits: 4 GB is 4,000,000,000 bytes, and 8 bits per byte makes 32,000,000,000 bits. 2. Effective speed: 90% of 100 Mbps is 90,000,000 bits per second, which the panel shows as 90 Mbps. 3. Time: 32,000,000,000 bits divided by 90,000,000 bits per second is **355.6 seconds**, shown as 5 minutes and 56 seconds. 4. Throughput: 90 Mbps moves 11.25 MB a second, or **675 MB** a minute, against a file of 4,000 MB. At 100% efficiency the same file would take 320 seconds, so the 90% allowance adds 35.6 seconds. From there, the comparison table runs from 35.6 seconds on the Fiber 1 Gbps preset to 59.3 minutes on DSL 10 Mbps. On screen, that last figure reads 59 minutes and 16 seconds. ## What Your Download Time Means Your result assumes one steady rate from start to finish. Measured speed, however, can land above or below the advertised figure, and the efficiency input stands in for that gap. Data on that gap comes from the FCC’s [Thirteenth Measuring Broadband America report](https://www.fcc.gov/reports-research/reports/measuring-broadband-america/measuring-fixed-broadband-thirteenth-report). It rests on validated data collected in September and October 2022 from fixed internet service providers (ISPs). In that report, eight measured download speeds were **100% or better** than advertised speeds during the peak hours (7 p.m. to 11 p.m. local time). Meanwhile, the four other ISP/technologies provided between 86% to 90% of their advertised speed. That [Measuring Broadband America program](https://www.fcc.gov/general/measuring-broadband-america) ran between 2011 and 2023 and is currently not collecting additional data, so these are the latest figures it produced. They describe wired home connections, not Wi-Fi or mobile links. Treat them as a range to try in the efficiency input, not a forecast for any one line. A similar caveat sits on the FCC’s [broadband speed guide](https://www.fcc.gov/consumers/guides/broadband-speed-guide). Its figures are rough guidelines and are not based on surveys or experiments conducted by the FCC. It also says that speeds are based on running one activity at a time. Four limits apply to the calculator too: - It assumes a steady rate from start to finish, with no ramp-up, pauses or server limits. - It models one transfer; other devices and downloads share the same connection. - Its seven connection presets are round illustrative speeds, not measured speeds for those technologies. - It estimates time only. A fast download says nothing about whether the file is what it claims to be. Meanwhile, files pulled over a café or hotel network carry separate risks, which the guide to [public Wi-Fi security risks](/public-wifi-security-risks/) sorts into real and overstated ones. ## GB vs GiB: Why 4 GB Can Mean Three Sizes A “4 GB” label can describe three different amounts of data, and each gives a different download time. NIST traces the confusion to early computing, when professionals started using the SI prefix “kilo” to mean 1024. Its summary is blunt: “The result is that today “everybody” does not “know” what a megabyte is.” NIST names three megabytes in use. Memory makers mostly mean **1,048,576 bytes**. Storage makers usually mean 1,000,000 bytes. Floppy disks added one more: the familiar “1.44 MB” diskette used a third megabyte of 1,024,000 bytes. IEC prefixes such as kibi, mebi and gibi now separate the binary sizes, though NIST notes they are not part of the International System of Units (SI). | Reading of “4 GB” | Bytes | Time at 100 Mbps and 90% efficiency | |---|---|---| | Decimal gigabytes (the calculator’s GB) | **4,000,000,000** | **355.6 seconds** (5 minutes, 56 seconds) | | 4 × 1,024 megabytes (mixed reading) | **4,096,000,000** | **364.1 seconds** (6 minutes, 4 seconds) | | Gibibytes (the calculator’s GiB) | **4,294,967,296** | **381.8 seconds** (6 minutes, 22 seconds) | *Source: NIST, Prefixes for binary multiples; times from the calculator’s formula* The mixed reading is the common slip: 1,024 megabytes to the gigabyte, then decimal megabits for the speed. Pick GiB in “Size unit” when a size comes from software that counts in powers of 2. Instead, pick GB when it comes from a storage label or a download page that counts in powers of 10. For the scale of data people now keep online, see the [cloud storage usage statistics](/cloud-storage-usage-statistics/). ## Mbps vs MB/s: Reading a Connection Speed Divide megabits per second by 8 to get megabytes per second: 100 Mbps is at most **12.5 MB/s**. FCC guidance quotes the minimum download speed (Megabits per second, or Mbps), a bit rate, while a file’s size is counted in bytes. Still, either unit works here. Pick KB/s, MB/s or GB/s in “Speed unit” to enter a rate in bytes, and it multiplies by 8 before dividing. For scale, the FCC’s March 2024 benchmark sets download speeds of 100 megabits per second and upload speeds of 20 megabits per second. That is a four-fold increase from the 25/3 Mbps benchmark set by the Commission in 2015. On mobile networks, the FCC assessed 5G coverage at minimum speeds of 35/3 Mbps. For wireless trends, the [5G statistics](/5g-statistics/) track subscriptions, coverage and measured speeds. ## How Long Does It Take to Download 1 GB? About a minute and a half at 100 Mbps. One gigabyte is 8,000,000,000 bits, which takes **88.9 seconds** at 90% efficiency, shown as 1 minute and 29 seconds. At the FCC guide’s minimum of 10 Mbps for file downloading, the same gigabyte takes 14.8 minutes, shown as 14 minutes and 49 seconds. Read as 1 GiB, either time grows by 7.4%. For example, load the “Examples” chip for a 4 GB game update to see a bigger file. Steam’s user base and concurrency records are in the [Steam statistics](/steam-statistics/). ## Why Is a Download Slower Than the Advertised Speed? Three things explain most of the gap: units, headers and the speed the line delivers. A 100 Mbps plan tops out at 12.5 MB/s in a window that counts bytes. Then TCP/IP headers take 2.7% of each full-size packet even with no options. Measured speed is the last factor. In the FCC’s Thirteenth Report, four of the 12 ISP and technology configurations delivered between 86% to 90% of their advertised speed at peak hours. The report also scores consistency with an “80/80” metric. It records the minimum percentage of the advertised speed experienced by at least 80% of subscribers for at least 80% of the time at peak. In the report’s words, the lowest performing technology, by this measure, was DSL, with providers achieving between **63% to 72%** of the advertised speed. For instance, entering 86 in “Real-world efficiency” stretches the 4 GB example to 372.1 seconds, or 6 minutes and 12 seconds. ## Sources Used on This Page - [Prefixes for binary multiples](https://physics.nist.gov/cuu/Units/binary.html), NIST. - [Measuring Fixed Broadband: Thirteenth Report](https://www.fcc.gov/reports-research/reports/measuring-broadband-america/measuring-fixed-broadband-thirteenth-report), FCC. - [Measuring Broadband America](https://www.fcc.gov/general/measuring-broadband-america), FCC. - [FCC Increases Broadband Speed Benchmark](https://docs.fcc.gov/public/attachments/DOC-401205A1.txt), FCC. - [Broadband Speed Guide](https://www.fcc.gov/consumers/guides/broadband-speed-guide), FCC. - [Transmission Control Protocol (TCP) specification](https://www.rfc-editor.org/rfc/rfc9293.html), IETF. - [Internet Protocol specification](https://www.rfc-editor.org/rfc/rfc791.html), IETF. - [Transmission of IP Datagrams over Ethernet Networks](https://www.rfc-editor.org/rfc/rfc894.html), IETF. ## Is there anything else my agent or I should know about this page? Yes. The calculator runs in your browser and nothing you enter reaches our server. It converts the file size to bits and divides by the connection speed times the efficiency you set. Megabytes are decimal unless you pick MiB, GiB or TiB. The efficiency setting stands in for protocol overhead, Wi-Fi conditions and a busy network, none of which the tool measures. Three things sit outside it: the sending server’s own speed limit, a connection speed that changes during the download, and a test of your actual line, so the result is an estimate rather than a measurement. SQ Magazine publishes the page for information. A transfer estimate helps you plan; it promises no download speed from any provider. ## Conclusion At 100 Mbps and 90% efficiency, a 4 GB file takes **5 minutes and 56 seconds**. By contrast, read as 4 GiB, it takes 6 minutes and 22 seconds. Try the “Examples” chips, switch “Size unit” between GB and GiB, or lower “Real-world efficiency” toward the FCC’s measured range. For a gamer queuing a large update, the estimate sets expectations before the progress bar does. For an IT team moving backups or disk images, the GB or GiB choice alone shifts the plan by 7.4%. The FCC reviews broadband in an annual assessment, so the benchmark behind the default speed can change. To compare a result with typical connections worldwide, the [internet statistics](/internet-statistics/) track average fixed broadband speeds by country. ## More Security Calculators [All security calculators (2) →](https://sqmagazine.co.uk/tools/) - [ Downtime a year At 99.9% 8h 45m 58s Security In your browser Uptime Calculator Downtime an uptime target allows, from a day to a year. 43m 50sPer average month (30.44 days) → ](https://sqmagazine.co.uk/uptime-calculator/) - [ Network 192.168.1.10/24 192.168.1.0/24 Network In your browser IP Subnet Calculator Network, broadcast, host range and mask for any IPv4 block. 254Usable hosts → ](https://sqmagazine.co.uk/subnet-calculator/)