Seeding and share ratios explained

Seeders, leechers and peers

Why seeding matters

BitTorrent was designed so that the original source doesn't carry the whole load. The protocol specification, BEP 3, explains that downloaders upload to each other, so the burden on the original source grows only a little as more people join. That only works if people upload. When the last seeder leaves and no one has a full copy, the torrent stalls.

Legal projects ask for this explicitly. Debian's torrent page says: "If you can, please leave your client running after your download is complete, to help others download images faster!" Older swarms can die out when people stop seeding. Archives with web seeds, such as the Internet Archive, avoid the problem because their servers always seed.

How BitTorrent rewards uploaders

BitTorrent clients decide whom to upload to with a system called choking, described in BEP 3. Every ten seconds or so, a client reviews its connections and uploads to the four interested peers giving it the best download rates. It also picks one extra peer at random every 30 seconds or so, called an optimistic unchoke, so newcomers get a chance. A peer that has finished downloading ranks by upload rate instead. The result is often called tit-for-tat: peers who upload more tend to get faster downloads.

What's a good share ratio?

On public swarms there's no rule. A ratio of 1.0, uploading as much as you downloaded, is a common courtesy target. Private trackers, which are invitation-only communities, set their own ratio rules for members.

How to set seeding limits

1. Open your client's seeding or ratio settings In qBittorrent, the share ratio limiting section lets you choose the ratio (uploaded divided by downloaded) to seed to.
2. Pick what happens at the limit qBittorrent can pause or remove the torrent once it reaches the ratio you set.
3. Set an upload speed cap Leave enough upload capacity for calls and browsing. A full upload link can slow everything else on your connection.
4. Keep peer discovery on for legal torrents DHT and peer exchange (PeX) help find more peers without relying on a tracker; qBittorrent's documentation describes both.

Seeding and the law

Seeding is uploading, and uploading is distribution. For legal content, that's fine and helpful. For copyrighted works shared without permission, it's the part that most clearly infringes. The EU's Court of Justice ruled in 2021 (Mircom, C-597/19) that uploading pieces through BitTorrent counts as making a work available to the public, even if the pieces are unusable on their own. In Japan, uploading carries heavier penalties than downloading: up to ten years in prison. Read is torrenting illegal?

Turning off seeding doesn't avoid this, because clients upload pieces while still downloading. The way to stay legal is to share legal content. See legal torrent sources.

Seeding and privacy

While you seed, your IP address is visible to every peer that connects. A VPN shows peers the VPN's address instead and hides the traffic from your internet provider. It doesn't change whether sharing a file is legal. If you use one, bind your client to it and turn on the kill switch; see the safe torrenting guide.