Mbps↔MB/s↔Gbpsを変換し、任意のファイルサイズ・回線速度でのダウンロード時間を計算。実運用時のオーバーヘッドや、4K動画・OSインストール・ゲームパッチなどのファイルサイズプリセットにも対応。
| 変換 | 値 |
|---|
1バイト = 8ビット。ISP(プロバイダー)は速度をメガビット毎秒(Mbps)で表示しますが、ファイルサイズはメガバイト(MB)で表されます。MB/s = Mbps ÷ 8。時間 = ファイルサイズ ÷ 転送速度。ストレージ容量やISPの広告表記はSI接頭辞に従うため、ここでは10進法(1 GB = 1,000 MB)を使用しています。
実際の通信では、TCP/IPヘッダーや再送、サーバー側の転送速度のばらつきなどにより約10%のオーバーヘッドが生じます。理論上の時間 × 1.111 ≈ 実際の時間の目安になります。
Download time = file size in bytes divided by (bits per second / 8). Every unit here is decimal SI rather than binary: 1 Mbps is 1,000,000 bits per second and 1 GB is 1,000,000,000 bytes, matching how ISPs advertise speed and how drives are labelled. Tick Apply ~10% real-world overhead and the time is multiplied by 1.111, the reciprocal of 90% goodput, covering TCP and IP headers, retransmits and bursty servers.
The speed Unit field is the one people get wrong. Kbps, Mbps and Gbps are bits; KB/s, MB/s and GB/s are bytes, and the eightfold gap between them is the whole reason this tool exists. Defaults are 100 Mbps against a 5 GB file, which comes out at 6m 40s. Six presets fill the file size in: MP3 song (5 MB), 1080p movie (5 GB), 4K movie (25 GB), OS install (5 GB), Game patch (50 GB) and AAA game (100 GB).
This is a straight division, so it assumes you hold your full advertised line rate for the entire transfer. It models nothing about the source server's own upload cap, Wi-Fi loss, evening congestion, disk write speed, or TCP slow start at the beginning of a connection. The overhead option is a single flat 10% allowance rather than a protocol simulation, and the conversion table always lists both the theoretical and the padded time regardless of the checkbox.
12.5 MB/s, because there are eight bits in a byte and the tool uses decimal megabits. The conversion table prints that directly, alongside the same speed expressed in Mbps and Gbps, whichever unit you originally typed in.
At 100 Mbps, about 2h 13m theoretically, or roughly 2h 28m once the 10% overhead allowance is applied. The AAA game (100 GB) preset fills the file size in for you, so you only need to set your line speed.
1,000. Kilo, mega, giga and tera are all powers of ten here, for both speeds and file sizes, because ISPs and drive manufacturers use SI prefixes. Your operating system may report the very same file as a smaller number of gigabytes.
The maths assumes your full line rate end to end. In practice the source server may throttle you, Wi-Fi and peak-time congestion cut throughput, and connections need time to ramp up. The overhead checkbox only covers protocol overhead, around 10%.
It is a fixed reference point: how long a single gigabyte takes at whatever speed you entered, independent of the file size field. Useful for mental arithmetic, since you can multiply it by however many gigabytes you actually need to move.
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