RTCDataChannel: bufferedAmount property

The read-only RTCDataChannel property bufferedAmount returns the number of bytes of data currently queued to be sent over the data channel. The queue may build up as a result of calls to the send() method. This only includes data buffered by the user agent itself; it doesn't include any framing overhead or buffering done by the operating system or network hardware.

The user agent may implement the process of actually sending data in any way it chooses; this may be done periodically during the event loop or truly asynchronously. As messages are actually sent, this value is reduced accordingly.

Note: Closing the data channel doesn't reset this count, even though the user agent purges the queued messages. However, even after closing the channel, attempts to send messages continue to add to the bufferedAmount value, even though the messages are neither sent nor buffered.

Whenever this value decreases to fall to or below the value specified in the bufferedAmountLowThreshold property, the user agent fires the bufferedamountlow event. This event may be used, for example, to implement code which queues more messages to be sent whenever there's room to buffer them.


The number of bytes of data currently queued to be sent over the data channel but have not yet been sent.


The snippet below includes a function which changes the contents of a block with the ID "bufferSize" to a string indicating the number of bytes currently buffered on an RTCDataChannel.

const dc = peerConnection.createDataChannel("File Transfer");

// …

function showBufferedAmount(channel) {
  const el = document.getElementById("bufferSize");

  el.innerText = `${channel.bufferedAmount} bytes`;


WebRTC: Real-Time Communication in Browsers
# dom-datachannel-bufferedamount

Browser compatibility

BCD tables only load in the browser

See also