Why are there two different units — bits and bytes?

Network speeds are measured in bits per second (Mbps, Gbps) while file sizes are measured in bytes (MB, GB). There are 8 bits in 1 byte. This calculator converts between them automatically, so you can mix units freely.

What is the efficiency (overhead) setting?

Real-world transfers never reach the theoretical line speed because of TCP/IP headers, retransmissions, encryption overhead, and protocol handshakes. 85% is a conservative estimate for most broadband connections. Adjust it downward for lossy links or upward for local wired transfers.

Does the calculator use 1000-based or 1024-based units?

Network speeds use SI (decimal) prefixes: 1 Mbps = 1,000,000 bits/s. File sizes use binary prefixes by default: 1 GB = 1,073,741,824 bytes. The calculator uses these standard conventions, which matches how ISPs advertise speeds and how operating systems report file sizes.

Why is my actual download speed slower than my plan speed?

ISP speeds are theoretical maximums shared across peak-hour users, affected by Wi-Fi interference, distance from the exchange, and server-side throttling. Use the efficiency slider to model a realistic share of your headline speed.

Can I calculate upload time separately from download time?

Yes. Simply enter your upload speed (typically lower than download on ADSL/cable) in the speed field. The formula is identical for both directions.

Bandwidth Calculator

Name: Bandwidth Calculator
Availability: InStock
Author: Nham Vu

Enter a file size and connection speed to calculate transfer time, or enter a file size and target time to calculate the required bandwidth.

File Size

Connection Speed

Link Efficiency: 85%

Lossy / Wi-Fi Ideal wired

Enter values on the left and press Calculate

Transfer Time

File Size

Connection Speed

Effective Throughput

Data Transferred

Transfer Time at Common Speeds

Connection	Speed	Transfer Time

Summary

Enter a file size and connection speed to calculate transfer time, or enter a file size and target time to calculate the required bandwidth.

How it works

Choose a calculation mode: Transfer Time (given speed) or Required Speed (given time).
Enter the file size and select its unit (KB, MB, GB, TB).
For Transfer Time mode, enter the connection speed and select its unit (Kbps, Mbps, Gbps).
For Required Speed mode, enter the target transfer time in hours, minutes, and seconds.
The result updates instantly with a human-readable breakdown.
Use the efficiency slider to account for real-world protocol overhead (default 85%).

Use cases

Estimate how long a large software download will take on your current connection.
Plan backup windows by calculating overnight transfer feasibility.
Determine the minimum ISP plan needed for a given file-transfer SLA.
Quickly compare transfer times across different cloud storage tiers.
Validate whether a site-to-site VPN link can handle expected throughput.
Help clients understand why large video uploads take so long.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu