The read-only property is an unsigned 64-bit integer value indicating the total size of the data being processed or transmitted. In the case of an HTTP transmission, this is the size of the body of the message (the Content-Length), and does not include headers and other overhead.

If the event's lengthComputable property is false, this value is meaningless and should be ignored.


let value =;


Specification Status Comment
The definition of 'ProgressEvent.lengthComputable' in that specification.
Living Standard

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
totalChrome Full support YesEdge Full support 12Firefox Full support 3.5IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes


Full support  
Full support
No support  
No support

See also