Download Time Calculator

How to use

1. 1Pick a calculation mode: Size + speed gives transfer time, Size + time gives the line rate you need.
2. 2Type a file size and choose a unit (KB, MB, GB, TB in decimal SI, or KiB, MiB, GiB, TiB in binary IEC), or tap a common file preset.
3. 3Type a connection speed in Mbps, Gbps, or MB/s, or tap a connection preset (cable, fiber, 5G, Wi-Fi, gigabit). For target-time mode, type the deadline as HH:MM:SS or 1h 30m.
4. 4Choose a real-world efficiency factor (100, 95, 85, 70, or 50 percent) to account for TCP overhead and Wi-Fi loss; 85% is a reasonable wired default.
5. 5Read the friendly duration, the HH:MM:SS clock form, and the comparison grid showing the same file at common speed tiers; copy any value with the Copy buttons.

About this tool

Download Time Calculator estimates how long a file transfer takes over any internet or local connection. Set a file size and a connection speed to get the transfer time, or flip the calculation around: set a file size and a target time, and the tool returns the connection speed you need to make that deadline. Both directions account for real-world efficiency: ISPs advertise a peak line rate (the bits per second your modem can theoretically push), but actual throughput is lower because of TCP/IP framing, retransmissions, server caps, congestion, Wi-Fi loss, and contention from other devices on the same link. The efficiency presets cover the four typical scenarios (100% pure line rate, 95% wired with light overhead, 85% real-world wired or strong Wi-Fi, 70% typical Wi-Fi or busy network, 50% weak Wi-Fi or distant server) and the math reflects whichever you pick. Sizes can be entered in either base 10 SI units (KB, MB, GB, TB) used by storage vendors and most file managers or base 2 IEC units (KiB, MiB, GiB, TiB) used by RAM and many operating systems, with the difference made explicit so you do not silently mix them. Speeds can be entered in either bits per second (bps, Kbps, Mbps, Gbps), the way ISPs advertise capacity, or in bytes per second (B/s, KB/s, MB/s, GB/s), the way download managers and browsers report progress, with a one-click conversion between the two. Common file-size and connection-speed presets cover everything from a 4 MB photo to a 1 TB drive image and from a 56k modem to a 10 Gbps fiber link, and a comparison panel shows the same file at six common speed tiers (10 Mbps, 25 Mbps, 100 Mbps, 300 Mbps, 1 Gbps, 10 Gbps) so you can see how an upgrade pays off. Useful for anyone deciding which internet plan to buy, scheduling overnight backups, sizing cloud egress for a customer migration, planning a video shoot upload, estimating Steam or App Store install times, debugging a slow transfer, or simply translating between the Mbps an ISP shows on the bill and the MB/s a browser shows during the actual download. Everything runs locally in your browser, so the file sizes and target times you type here never leave your device.

Free to use. Works in your browser. No signup, no login.