Download Time Calculator
Estimate how long a download will take from the file size and your connection's download speed.
Inputs
Actual throughput vs. advertised speed (protocol overhead, congestion).
Estimated Download Time
1m 34.1s
Ideal Time (100% speed)
1m 20s
Effective Speed
85.00Mbps
Time in Seconds
94.12s
Step by step
Values used
File Size = 1,000 MB; Download Speed = 100 Mbps; Real-World Efficiency = 85
Download time
time = (file_size_MB × 8) / (download_speed_Mbps × efficiency)
Estimated Download Time
= 1m 34.1s
Ideal Time (100% speed)
= 1m 20s
Effective Speed
= 85.00 Mbps
Time in Seconds
= 94.12 s
How it works
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.
Formula
Download time
time = (file_size_MB × 8) / (download_speed_Mbps × efficiency)
- S_MB
- File size in megabytes
- v_Mbps
- Download speed in Mbps
- \eta
- Real-world efficiency factor
Frequently Asked Questions
Why is my download slower than my advertised internet speed?
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.
Why multiply the file size by 8?
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.
How can I speed up a large download?
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.