Send files between two computers over the internet

Last updated: 2026-08-05

Sending a file to another computer usually means uploading it somewhere first — a cloud drive, an email attachment, a chat app — and hoping the recipient can get it back out again. Relayium skips that storage step: browsers connect directly on the same LAN, while cross-network transfers use a TURN relay that carries only end-to-end encrypted ciphertext and keeps no server-side realtime content copy or history.

This guide covers both cases — two computers on the same network, and two computers on completely different networks (different homes, offices, countries) — and shows exactly what each side needs to do.

The direct approach: no cloud in the middle

Relayium runs entirely in the browser at relayium.com. There is nothing to install on either computer, and no third-party storage sits between you and the recipient: the file streams from one browser to the other and is never written to a server — not even when the two networks require the stream to pass through a relay, which forwards the bytes without keeping a copy or holding a key.

That matters for two reasons: speed (you are not bottlenecked by someone else's upload/download quota) and privacy (no copy of your file sits on a company's servers waiting to be requested, breached, or forgotten about).

Same network vs. across the internet

If both computers are on the same Wi-Fi or LAN, Relayium finds them automatically — open relayium.com on both, and no account is needed on either side.

If the two computers are on different networks — your desktop at home and a colleague's laptop across the country, for instance — automatic discovery cannot reach across the internet, so Relayium uses a short pairing code instead. The person sending signs in to mint that code; the person receiving never needs an account, whether they type the code in or just open the link it generates. The code is good for five minutes, so have both devices in front of you before you generate one.

Step by step: send a file across the internet

Here is the full flow for two computers on different networks:

1. On the sending computer, open the realtime transfer page and sign in.

   https://relayium.com/cross-network

2. Pick the files or the folder to send — up to 1,000 files per batch — and create the pairing code. The card then shows the six digits, a copy-link button, a QR code, and a countdown.

   Your pairing code — read it to the other person
   483920
   pairing code expires in 4:52

3. Pass the code or the link to the other person however is convenient — read it out, text it, paste it in chat. The link carries the same code in its fragment, so sharing either one is the same act.

   https://relayium.com/cross-network#c=483920

4. On the receiving computer, open that link, or open the same page, type the six digits and press “Connect”. There is no sign-in on this side.

   https://relayium.com/cross-network

5. The transfer starts once the other device joins. Leave both tabs open until the file counter reaches the end: the countdown governs new joins only, so it stopping does not cut a transfer that is already running. Turning on “Advanced verification” before you start adds a verification code (SAS) to compare — a match confirms the keys were not replaced and both computers joined the same end-to-end encrypted session; it does not prove which network path carries the ciphertext.

Relayed
File 1/1

When the code is refused, or the transfer stops

A cross-network transfer has more moving parts than a same-network one — a code with a life span, an account, a relay allowance — and each of them says which it is on the pairing card rather than failing silently. Read that card first.

Across networks: the encrypted relay

Two browsers on the same network connect directly to each other. Across networks — where corporate firewalls and strict NATs routinely block a direct path — Relayium carries the encrypted stream over a TURN relay instead, so the transfer connects reliably.

The relay only ever sees ciphertext: the file is encrypted end-to-end (X25519 key exchange plus AES-256-GCM) before it ever leaves the sending browser, so the relay cannot read it any more than a random computer on the internet could. If the connection drops partway through, the transfer resumes instead of starting over.

How many files, and how large

You can send up to 1,000 files in one batch, folder structure included. There is no server-side size cap — the practical ceiling is set by the receiving browser.

A browser with the File System Access API — Chrome or Edge on the desktop — streams incoming data straight to disk, so multi-gigabyte files are fine. Firefox and Safari don't have that API, so a batch received there is assembled in memory instead, and Relayium warns you before you accept once it goes past roughly 256 MB: a deliberately conservative estimate rather than a measured limit, since the real ceiling depends on the machine's memory, its OS and what else is open. Each file is also checked end-to-end with a SHA-256 hash, so you know what arrives is byte-for-byte what was sent.

Frequently asked questions

Is it really peer-to-peer, or does the file pass through a server?

It is peer-to-peer in the sense that matters: the file streams browser to browser and is never stored on a server. On the same LAN the two browsers connect directly to each other. A cross-network pairing-code transfer uses TURN by design, but the relay only forwards end-to-end encrypted ciphertext in flight: it cannot read or decrypt the file and keeps no server-side realtime content copy or history.

Do both people need an account?

No. On the same network, neither side needs an account. Across different networks, the person sending signs in to create the pairing code — that's what lets Relayium mint and manage the code — but the person receiving never needs an account, whether they type in the code or just open the link.

Does it work across different networks and countries?

Yes. The pairing code exists specifically for this case: two computers that aren't on the same local network, wherever each one is in the world. That route runs over an encrypted TURN relay rather than a direct link, and it does so deliberately: Relayium takes the relay so that getting past NATs and firewalls never depends on a direct path being available.

Is there a limit on file size or how many files I can send?

You can send up to 1,000 files in a single batch. No Relayium server imposes a size cap, so the limits that remain are practical ones: Chrome or Edge on the desktop streams the batch straight to disk, and what bounds it there is the browser, the operating system, the free space on that disk and how long the live session stays up. Firefox and Safari hold the batch in memory instead, where Relayium warns you above roughly 256 MB — a cautious estimate rather than a hard ceiling; the real one depends on the machine.

Keep reading

• Transfer files by scanning a QR code
• Send files between devices on the same Wi-Fi
• What is peer-to-peer file transfer?
• How to send large files without the cloud
• Relayium