Why is my download speed in MB/s slower than my ISP's Mbps rating?

Internet Service Providers advertise speed in Megabits per second (Mbps, with a lowercase 'b'), whereas browsers and game launchers display download speeds in MegaBytes per second (MB/s, with an uppercase 'B'). Since there are 8 bits in 1 Byte, a 100 Mbps broadband plan delivers a theoretical maximum download speed of 12.5 MB/s.

What is network protocol overhead?

TCP/IP, Ethernet frame headers, Wi-Fi encryption packets, and packet acknowledgments consume approximately 8% to 12% of total transmitted bandwidth. Factoring in a 10% realistic overhead provides an accurate ETA for real-world broadband connections.

How long does it take to download a 100 GB game on a 100 Mbps connection?

On a 100 Mbps connection with realistic 10% TCP protocol overhead (effective rate of ~11.25 MB/s), downloading a 100 GB game takes approximately 2 hours, 28 minutes.

⏱️ File Transfer & Bandwidth Time Estimator

Download Time Calculator

Calculate the exact time required to download or upload games, 4K video, backups, and operating system installers based on your internet connection speed.

File / Game Size:

Popular Presets:

Internet Connection Speed:

Common Broadband Speeds:

Real-world TCP/IP Protocol Overhead: 10% (Realistic Broadband)

Accounts for packet headers, TCP acknowledgments, and wireless signal variance. Set to 0% for theoretical wire speed.

Estimated Download Completion Time: Rate: 11.25 MB/s

1 hr 14 mins

Days

Hours

Minutes

Seconds

How Fast Would This File Download on Other Plans?

Broadband Plan	Effective Speed (MB/s)	Download Time

Why Does 100 Mbps Only Download at 12.5 MB/s? (Bits vs Bytes Explained)

The number one confusion with internet speeds is the difference between a bit (b) and a Byte (B):

1 Byte = 8 bits.
ISPs always market speeds in Megabits per second (Mbps) because the number is 8 times higher and looks faster.
Files, hard drives, Steam, and browsers measure sizes in MegaBytes (MB) and GigaBytes (GB).
To find your real download rate, divide your ISP speed by 8. A 100 Mbps connection gives a maximum theoretical speed of 100 ÷ 8 = 12.5 MB/s.