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Download Time Calculator
A 1 GB file on a 100 Mbps connection does not take 10 seconds — it takes 80, because file sizes are measured in bytes and speeds in bits, and there are 8 bits in a byte. Enter a file size and a speed to get the download time, or flip the mode to find the speed you need or how much you can download in the time you have.
Units here are decimal, as internet providers and file listings use them: 1 GB = 1,000 MB and 1 Mbps = 1,000,000 bits per second. Some operating systems show sizes in binary units (1 GiB = 1,024 MiB), which is about 7% larger — a file your computer calls 1 GiB is 1.074 GB here. Efficiency accounts for protocol overhead and congestion: a connection rarely sustains its advertised speed end to end.
How it works
Download time comes from three numbers: the file size in bytes, the speed in bits per second, and the fact that 1 byte = 8 bits. Convert the size to bits (multiply bytes by 8), then divide by the speed: time in seconds = size in bits ÷ speed in bits per second. Real connections never hit their advertised speed, so the result is divided by the efficiency (95% means multiply the time by 100/95). Worked example: a 1 GB file is 1,000,000,000 bytes = 8,000,000,000 bits; at 100 Mbps (100,000,000 bits per second) that is 8,000,000,000 ÷ 100,000,000 = 80 seconds = 1 minute 20 seconds. Worked example 2: a 4.7 GB film at 50 Mbps takes 4,700,000,000 × 8 ÷ 50,000,000 = 752 seconds = 12 minutes 32 seconds. Flip the formula to find a speed: 2 GB in 5 minutes needs 2,000,000,000 × 8 ÷ 300 = 53.3 Mbps.
Frequently asked questions
Why is my download slower than my advertised speed?
Advertised speeds are maximums under ideal conditions. Protocol overhead, Wi-Fi signal, server load, other devices on your network and congestion all take a cut — a real-world efficiency of 85-95% is normal, which is why this calculator lets you set one. If downloads are far slower still, test your speed at a different time of day and check whether another device is streaming or updating.
What is the difference between MB and Mb?
Capital B means bytes, lowercase b means bits — and there are 8 bits in a byte. File sizes are quoted in bytes (MB, GB) while internet speeds are quoted in bits (Mbps). So a 100 Mbps connection moves at most 12.5 MB/s, and a 1 GB file takes 80 seconds at that speed, not 10.
Are these decimal or binary gigabytes?
Decimal, as providers and file listings use them: 1 GB = 1,000 MB, 1 Mbps = 1,000,000 bits per second. Windows and some tools use binary units (1 GiB = 1,024 MiB), so a file your computer calls 1 GiB is 1.074 GB here and takes about 7% longer than the decimal figure.
How long does a 1 GB file take to download?
At 100 Mbps, 80 seconds (1 minute 20 seconds) at 100% efficiency. At 25 Mbps it is 5 minutes 20 seconds; at 1 Gbps it is 8 seconds. A 4.7 GB film at 50 Mbps takes about 12 minutes 32 seconds.
How fast do I need to stream 4K video?
Netflix and YouTube recommend about 25 Mbps for a single 4K stream, 5 Mbps for HD and 3 Mbps for standard definition — per simultaneous stream. For a household, add the streams together and leave headroom for downloads and video calls.
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