Enter a file size (KB/MB/GB/TB) and a speed (MB/s, KB/s or Mbps) and see the transfer time as you type. Handles the bytes-versus-bits conversion that makes a 100 Mbps line move ~12.5 MB/s, not 100 - the usual source of a wildly optimistic estimate. Runs fully client-side. Imported Claude artifact. Source: https://github.com/simonw/tools (transfer-time.html, Apache-2.0).

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Details

PricingCompletely free

Security scanClean — skill and frontend scanned

Source simonw/tools

Created2026-08-25

Updated2026-08-25

View source prompt + release files — fork-enabled apps share their full source

System prompt (SKILL.md)

---
name: transfer-time-calculator
description: Work out how long a file takes to move at a given speed, with the byte-versus-bit units kept straight.
metadata:
  tags:
    - artifact-import
    - utilities
  source_url: https://tools.simonwillison.net/transfer-time
  github_repo_url: https://github.com/simonw/tools
---

# Transfer Time Calculator

An imported Claude artifact. Enter a file size in KB, MB, GB or TB and a speed
in MB/s, KB/s or Mbps, and the transfer time appears as you type.

The reason this is worth a tool rather than mental arithmetic is the unit
mismatch: file sizes are quoted in bytes and connection speeds are quoted in
bits, so a "100 Mbps" line moves about 12.5 MB a second, not 100. Getting that
factor of eight wrong is the usual source of a wildly optimistic estimate. The
calculator handles the conversion between the two families for you.

Everything runs in the page. Nothing is uploaded, no model is called, and
nothing is metered.

Release files (files)

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