Understanding your download time result
The table below shows the effective transfer rate and the ideal time to download 1 GB (10⁹ bytes) at common connection speeds. Real-world times are typically 10–50% longer due to overhead and congestion.
| Connection speed | Effective rate | Time for 1 GB (ideal) |
|---|---|---|
| 10 Mbps | 1.25 MB/s | 13 min 20 s |
| 25 Mbps | 3.125 MB/s | 5 min 20 s |
| 50 Mbps | 6.25 MB/s | 2 min 40 s |
| 100 Mbps | 12.5 MB/s | 1 min 20 s |
| 500 Mbps | 62.5 MB/s | 16 s |
| 1,000 Mbps (1 Gbps) | 125 MB/s | 8 s |
- The calculation assumes a sustained, uninterrupted transfer at the entered speed. Protocol overhead, Wi-Fi signal quality, server limits and simultaneous users all reduce real throughput.
- File sizes here use decimal units (1 GB = 10⁹ bytes). Operating systems that report sizes in binary units (GiB) will show slightly smaller numbers for the same file.
- Advertised ISP speeds are 'up to' figures; a speed test at the time of download gives a more accurate input value.
What is download time and why does Mbps not equal MB/s?
Download time is the duration needed to transfer a file of a given size over a connection of a given speed. The single most important concept is the difference between bits and bytes: network speeds are quoted in megabits per second (Mbps, lowercase b), while file sizes are stored in megabytes or gigabytes (MB/GB, uppercase B). One byte equals 8 bits, so a 100 Mbps connection moves at most 12.5 megabytes per second — not 100.
This bits-versus-bytes distinction follows international unit conventions: the bit (bit) and byte (B) are distinct units of information, and SI prefixes such as mega (10⁶) and giga (10⁹) scale them decimally. A 50 GB file therefore contains 50 × 10⁹ bytes = 400 × 10⁹ bits, and dividing that bit count by the connection speed in bits per second gives the theoretical minimum transfer time.
Real downloads are slower than the theoretical minimum. Protocol overhead (TCP/IP headers, encryption), server throughput limits, Wi-Fi conditions and network congestion all reduce effective speed. Advertised broadband speeds are maximums measured under ideal conditions, which is why this calculator also shows the time at half the entered speed as a more conservative estimate.
How to use this download time calculator
- Enter the file size and select its unit (MB, GB or TB). These are decimal units: 1 GB = 1,000 MB.
- Enter your connection speed in Mbps — the number your internet plan or a speed test reports.
- Read the estimated download time, calculated from the ideal full-speed transfer.
- Check the half-speed estimate for a realistic upper bound, and the effective MB/s figure to see your speed in file-size units.
The formula behind download time
Download time equals the file size converted to bits, divided by the connection speed in bits per second. Because 1 byte = 8 bits, a size in megabytes is multiplied by 8 to get megabits before dividing by the Mbps speed.
Worked example: a 50 GB file on a 100 Mbps connection. The file contains 50 × 10⁹ bytes × 8 = 4 × 10¹¹ bits. Dividing by 100 × 10⁶ bits per second gives 4,000 seconds, which is about 1 hour 7 minutes. The effective transfer rate is 100 ÷ 8 = 12.5 MB/s, and at half speed the same file would take roughly 2 hours 13 minutes.
Common mistakes
- Confusing Mbps (megabits per second) with MB/s (megabytes per second) — they differ by a factor of 8, so a 100 Mbps plan delivers at most 12.5 MB/s.
- Expecting the full advertised plan speed: real throughput is reduced by protocol overhead, Wi-Fi conditions and server-side limits.
- Mixing decimal and binary size units — a file reported as 1 GiB by the operating system is about 7.4% larger than 1 GB.
- Forgetting that upload speed is often much lower than download speed on asymmetric connections, so sending the same file can take far longer.
Perguntas frequentes
How long does it take to download 1 GB at 100 Mbps?
About 80 seconds under ideal conditions. 1 GB is 10⁹ bytes = 8 × 10⁹ bits; divided by 100 × 10⁶ bits per second this gives 80 seconds, or 1 minute 20 seconds. Real downloads usually take somewhat longer because of protocol overhead and network conditions.
What is the difference between Mbps and MB/s?
Mbps means megabits per second and MB/s means megabytes per second. One byte is 8 bits, so divide Mbps by 8 to get MB/s: a 100 Mbps connection transfers at most 12.5 MB/s. Internet plans are marketed in Mbps because the number is 8 times larger, while file managers report sizes and transfer rates in bytes.
Why is my actual download slower than this calculator says?
The calculator gives the theoretical minimum time at the entered speed. Real transfers carry TCP/IP and encryption overhead, share bandwidth with other devices, and depend on the sending server's capacity and your Wi-Fi conditions. A common rule of thumb is to expect 50–90% of the advertised speed, which is why the calculator also shows a half-speed estimate.
Is 1 GB equal to 1,000 MB or 1,024 MB?
In the SI decimal convention used by this calculator and by storage and network vendors, 1 GB = 1,000 MB = 10⁹ bytes. The binary value 1,024 MiB corresponds to 1 GiB (gibibyte), a separate unit defined by IEC binary-prefix conventions. The difference between GB and GiB is about 7.4%.
How long would a 100 GB game download take on 50 Mbps?
About 4 hours 27 minutes under ideal conditions: 100 × 10⁹ bytes × 8 = 8 × 10¹¹ bits, divided by 50 × 10⁶ bits per second gives 16,000 seconds. At half the speed it would take roughly 8 hours 53 minutes, so overnight downloads are common for large games on mid-range connections.
Referências
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure), 9th edition, 2019 — decimal SI prefixes.
- ISO/IEC 80000-13:2008. Quantities and units — Part 13: Information science and technology — bit, byte, and binary prefixes.
- NIST Special Publication 811 (Thompson & Taylor). Guide for the Use of the International System of Units (SI), 2008.