Calculate how long a download will take based on file size and internet speed.
Download time is the file size converted to bits divided by the effective download speed. ISPs advertise speed in megabits per second (Mbps) while file sizes are usually shown in megabytes (MB), so the file size is first multiplied by 8 to convert MB to megabits. Real-world throughput is typically lower than the advertised link speed due to TCP/IP overhead, server limits, and network congestion, which the efficiency factor accounts for.
Download time
time = (file_size_MB × 8) / (download_speed_Mbps × efficiency)
ISPs advertise the theoretical maximum link speed in Mbps, but actual throughput is reduced by TCP/IP overhead, Wi-Fi interference, server-side bandwidth limits, and congestion at any hop between you and the source. The efficiency field lets you model this real-world drop, typically 70-95% of the rated speed.
File sizes are conventionally shown in bytes (MB, GB) while connection speeds are marketed in bits per second (Mbps). Since 1 byte = 8 bits, the file size in megabytes must be multiplied by 8 to get megabits before dividing by a Mbps speed.
Use a wired Ethernet connection instead of Wi-Fi, download from a server geographically closer to you or with a CDN, avoid other devices saturating the same link during the transfer, and check whether the source server itself is rate-limiting the connection.