Why are bits (Mbps) and bytes (MB/s) different?

Internet connection speeds are advertised in bits per second (Mbps). Files are measured in bytes. 1 byte = 8 bits, so 100 Mbps = 12.5 MB/s in theory and ~11 MB/s after overhead.

What's the difference between MB and MiB?

Decimal (SI): MB = 1,000,000 bytes. Binary (IEC): MiB = 1,048,576 bytes. Storage marketers use decimal; operating systems often use binary. Pick whichever matches your source.

Is the overhead slider accurate?

It's a flat-percentage approximation. Real overhead depends on protocol (HTTP/2, QUIC, raw TCP), packet loss, RTT, and parallelism. 5 % is reasonable for fast LAN, 10–15 % for high-RTT or lossy links.

Does this work for upload too?

Yes — the math is the same. Just enter your upload speed instead of download speed.

Bandwidth & Download Time Calculator

Compute any one of (transfer time, required throughput, transferable size) from the other two. Useful for sizing downloads on a slow connection, validating a backup window, estimating CDN cost, or sanity-checking a 'how long will this take' question. Bit-rate units (Mbps, Gbps) and byte-rate units (MB/s) are kept distinct — and decimal (KB = 1000) vs binary (KiB = 1024) prefixes are both supported. An overhead slider models the ~5–10 % loss from TCP/IP headers, ACKs, and framing.

—

Solve for

File size

Connection speed

Protocol overhead: 5%Approximate TCP/IP framing & retransmit loss. 5 % is typical for fast LAN, 10–15 % for high-latency links.

Speed presets

Estimated transfer time

6m 35s

Effective rate (bits/s):95.0 Mbps

Effective rate (bytes/s):11.9 MB/s

Decimal units (KB = 1000) and binary units (KiB = 1024) are both available — pick the one your source uses.

How to use

Pick a mode: solve for time, required speed, or transferable size.
Enter the two known values with units; the third updates live.
Use a connection preset (Wi-Fi 6, Gigabit, 4G LTE…) to fill in a typical speed.

Frequently asked questions

Why are bits (Mbps) and bytes (MB/s) different?: Internet connection speeds are advertised in bits per second (Mbps). Files are measured in bytes. 1 byte = 8 bits, so 100 Mbps = 12.5 MB/s in theory and ~11 MB/s after overhead.
What's the difference between MB and MiB?: Decimal (SI): MB = 1,000,000 bytes. Binary (IEC): MiB = 1,048,576 bytes. Storage marketers use decimal; operating systems often use binary. Pick whichever matches your source.
Is the overhead slider accurate?: It's a flat-percentage approximation. Real overhead depends on protocol (HTTP/2, QUIC, raw TCP), packet loss, RTT, and parallelism. 5 % is reasonable for fast LAN, 10–15 % for high-RTT or lossy links.
Does this work for upload too?: Yes — the math is the same. Just enter your upload speed instead of download speed.

Related tools

Data Transfer Rate Converter

Convert data rate between bit/s, kbit/s, Mbit/s, Gbit/s, Tbit/s and B/s, kB/s, MB/s, GB/s, TB/s — all at once.

Convert 0 0

Reading Time & Speaking Time Calculator

Estimate how long it takes to read or speak a text — adjustable WPM presets for slow, average, fast readers, TED, podcast.

Text 0 0

Subnet Calculator (IPv4 / CIDR)

Parse an IPv4 CIDR into network address, broadcast, netmask, wildcard, host range, and class. Shows binary breakdown and private/public status.

Network 0 0

HTTP Status Code Reference

Searchable list of every HTTP status code (1xx-5xx) with summary, RFC, when to use, and common pitfalls.

Network 0 0

User Agent Parser

Parse a User-Agent string into browser, engine, OS, device, and CPU. Detects 20+ bots including GPTBot, ClaudeBot, PerplexityBot.

Network 0 0

IPv4 Address Converter

Convert an IPv4 address between dotted-decimal, 32-bit integer, hex and binary — and see whether it's private, public, loopback and more.

Network 0 0