Transfer files between a Mac and a Windows PC

Last updated: 2026-08-07

Macs and PCs don't speak the same file-sharing language out of the box. AirDrop is Apple-only, Windows' network sharing wants both machines on a matching workgroup or domain, and neither one is exactly friendly to set up in five minutes when you just want to move one folder of project files from a MacBook to a Windows desktop.

Relayium sidesteps the whole compatibility question. Open the same page on both computers: on the same LAN the end-to-end encrypted files travel directly, while across networks a TURN relay carries ciphertext it cannot read or decrypt and keeps no realtime content copy or history. Nothing needs installing; the creator signs in for cross-network pairing, while the person joining never needs an account. Here's exactly how it works in both directions.

What you need before you start

What you need

A Mac with Safari or Chrome, and a Windows PC with Edge or Chrome — any modern browser on either side.
For the simplest path, both machines on the same Wi-Fi or Ethernet network. Mixing the two is fine: a wired PC and a Mac on the same router still share one public IP, which is what puts them in the same room.
The page open over https://relayium.com/ on both. Encrypted transfer needs HTTPS, and over plain http:// the page says so instead of listing devices.
For a large batch, Chrome or Edge on whichever machine is receiving. Only those can stream straight to disk and let you pick a target folder — Safari has no such API and has to assemble the batch in memory instead.
The files or folders to send — up to 1,000 files per batch.

Nothing to install on the Mac or the PC. On the same network there is nothing to sign up for either — the browser handles everything.

Mac and PC on the same network

If both computers are on the same office or home network, this is the fastest way to move files — no shared drive to mount, no permissions to fight with.

On the Mac, open the transfer page in the browser. On the Windows PC, open the same address.
```
https://relayium.com/
```
Compare the public IP in the status pill on both machines. One shared address is what puts them in the same room — a corporate VPN on the work laptop is the usual reason two machines on one office network report different ones.
```
Connected · this device MacBook · public IP 203.0.113.9
```
Each machine now appears to the other under “Nearby devices” — no Windows workgroup setup, no macOS file sharing to enable. On the sending computer, click the other one and press “Open workspace”. On a current browser that is the single action the card offers, because files, folders and messages all travel over the one encrypted connection it opens.
The workspace replaces that card. Send from the controls under its header: “Send files” for a batch of up to 1,000, “Send a folder” for a whole tree, or type into the message box — “Enter for a new line · ⌘/Ctrl+Enter to send” — and press “Send”. On the receiving side, read the line under the request: in Chrome or Edge it says the browser will ask where to save, so you pick the folder yourself, and in Safari or Firefox it says the files go to the browser's own Downloads. Then press “Accept”.
Watch the file counter run to the last file on both screens. To compare a verification code (SAS) before any bytes move, turn on “Advanced verification” on both machines first: a match confirms both joined the same end-to-end encrypted session, and it does not prove which network path carries the ciphertext. Left off, the session is still encrypted and there is simply no code to compare.

What a working transfer looks like

The other machine's card is gone by then — the workspace took its place — so the state is read off the workspace header: the machine you are connected to, a link state of “Connected”, and one path badge reading “LAN direct”. The counter ends on the last file of the batch.

In the folder you picked, the tree arrives with its relative paths intact. A name already present in that directory target is not overwritten: report.pdf lands next to it as report (1).pdf. That renaming is Relayium's own, and it applies only where the browser handed us a directory to write into — Chrome or Edge with the folder picker. Without the picker the naming belongs to that browser's download manager instead, and you read the result in its own list: chrome://downloads in Chrome, edge://downloads in Edge, about:downloads in Firefox.

Connected to ThinkPad · Connected · LAN direct
File 12/12

When one machine can't see the other

On this pair a work VPN and a managed office network are the two worth checking first. They are common first checks rather than the whole list, and everything below is decided by something already on the screen rather than by a support ticket.

Symptom, check, fix

Neither machine appears under “Nearby devices”, even though both are on the office Wi-Fi.

https://relayium.com/   # compare the public IP in the status pill on both machines

Two different public IP addresses mean two rooms, and a corporate VPN is one common cause: it carries one machine out through the company's address while the other leaves through the office router. A guest SSID that exits elsewhere is another, and they are not the only ones. If you are willing to change them, disconnect the VPN on that machine or leave the guest SSID, then reload https://relayium.com/ there. If the VPN has to stay up, a pairing code on https://relayium.com/cross-network reaches the other machine without dropping it.

Both machines show the same public IP and neither card appears.

https://relayium.com/   # the hint under the device list names the router setting

The network is separating its own clients. On a router that is yours, turn off “AP isolation / client isolation”; on a managed office network that you cannot change, pair the two machines with a code on https://relayium.com/cross-network instead.

The Mac warns, before you accept, that the whole batch has to be held in memory.

https://relayium.com/   # the line under the request says how this browser will save

Safari has no File System Access API, so it buffers the batch instead of writing it out, and Relayium warns past roughly 256 MiB. Receive the same batch in Chrome or Edge on that Mac: it streams each file straight to disk and asks you for a target folder first.

One file in a folder transfer fails on the Windows side while the rest arrive.

https://relayium.com/   # the counter names the file it is on when it stops

Windows forbids the characters \ / : * ? " < > | in a file name and macOS does not, so a name that is legal on the Mac can be impossible to create on the PC. Rename that file on the Mac — a colon in a date like 2026:08:05 is the usual offender — and send it again.

The transfer works but the badge reads “P2P direct” instead of “LAN direct”.

https://relayium.com/   # read the path badge in the workspace header

The two machines share a public IP without sharing a local hop, which is what two VLANs behind one office uplink look like. The transfer is still direct and still end-to-end encrypted; put both on the same subnet if you want the path to be your LAN rather than whatever route the browsers found.

On different networks: pairing and relay

The server generates exactly six decimal digits (0–9, including a leading zero). The sender signs in to create the code, while the person joining by code, link or QR never needs an account. It accepts new joins for five minutes; an already connected transfer is not cut off when that countdown ends.

Across networks, browsers use an encrypted TURN relay by design rather than trying a direct path first. The key stays on the two devices, so the relay forwards only end-to-end-encrypted ciphertext, cannot read the files and keeps no realtime content copy or history.

Sending a whole folder, not just single files

Moving a project folder from Mac to Windows (or back) usually means zipping it first. Relayium can send a folder directly, keeping its structure intact.

On the Mac, drag a folder in, or pick one from the file dialog — up to 1,000 files in the batch.
On a Windows PC using Edge or Chrome, the incoming folder is written straight into a directory you choose, structure preserved.
If the receiving browser doesn't support writing folders directly, the folder arrives as a single .zip that unpacks to the same layout.

Other ways to move files between Mac and Windows

Relayium isn't the only option — here are the honest trade-offs of the usual alternatives:

A USB flash drive works offline, but macOS and Windows don't always agree on a filesystem without reformatting, and it's one more physical object to keep track of.
Windows network sharing (SMB) can reach a Mac, but setting up workgroups, permissions, and firewall rules for a one-time transfer is more setup than the transfer is worth.
A cloud drive (OneDrive, iCloud, Google Drive) works when the other person is offline, but the file gets uploaded and then downloaded, counts against your storage quota, and the provider keeps a copy.
Email and chat apps are convenient but usually cap attachment size and aren't end-to-end encrypted for file sharing.

Will anything about the files change?

The contents do not. Relayium transfers the original bytes exactly as they are — no re-compression, no reformatting, no line-ending rewriting between the two operating systems — and a folder keeps its relative paths. Two things do not make the crossing, and both belong to the filesystem rather than to the transfer: Windows forbids characters that macOS allows, so a name legal on the Mac can be impossible to create on the PC, and POSIX permission bits, ownership and macOS extended attributes are not carried over — the receiving browser writes ordinary files under NTFS's own permission model.

Every file is checked end-to-end with a SHA-256 hash, so what lands on the Windows PC (or the Mac) is verified identical to what left the other machine. Large files are handled well too: a browser with the File System Access API — Chrome or Edge on the desktop — streams the download straight to disk with no size cap. 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. That number is a deliberately conservative estimate rather than a measured limit — where it actually breaks down depends on the machine's memory, its OS and how much else is open.

Frequently asked questions

Do I need to install anything on the Mac or the Windows PC?

No. Relayium runs entirely in the browser on both macOS and Windows. Open relayium.com on each machine and you're ready — nothing to download either way. On the same network a transfer needs no account at all; pairing across the internet only asks the sender to sign in.

Do both computers have to be on the same network?

No. Being on the same network is the fastest path because the two machines find each other automatically, but a pairing code connects a Mac and a Windows PC across the internet just as well — even from different cities. Either way the transfer stays end-to-end encrypted; the cross-network route just asks the sender to sign in first, and the receiver never needs an account.

Can I send a whole folder, not just individual files?

Yes. Drag in a folder and Relayium sends up to 1,000 files in the batch, preserving the folder structure. Chrome and Edge on Windows write it straight into a chosen directory; if the receiving browser can't write folders directly, it arrives as a single .zip with the same layout.

Will file permissions, line endings, or filenames get mangled crossing from Mac to Windows?

The bytes and the relative path inside a folder are unchanged, verified with a SHA-256 hash end-to-end, so nothing touches line endings or encoding — anything an application-level conversion would need to handle (like CRLF vs LF in a text file) is unchanged because the file itself is unchanged. Two things genuinely do not cross: a name containing one of the characters Windows forbids can't be created on the PC at all, and POSIX permissions, ownership and macOS extended attributes are not transferred, because the receiving browser writes ordinary files under NTFS's own model.

Is there a size limit?

Up to 1,000 files per batch. There's no server-side size cap at all — Chrome and Edge on the desktop stream straight to disk. Firefox and Safari lack the File System Access API, so a batch received in one of those is held in memory, and Relayium warns you above roughly 256 MB — a cautious estimate rather than a hard limit, since the real ceiling depends on the machine's memory and what else it is running.

Open Relayium on your Mac and your Windows PC and move your first files across — no install, and no account needed on the same network.

Try Relayium now