Finnnn, you are right.
From html5 specification,
http://www.w3.org/TR/2012/WD-html5-author-20120329/the-canvas-element.html#the-canvas-element
The canvas element has two attributes to control the size of the coordinate space: width and height.
These attributes, when specified, must have values that are valid non-negative integers.
The width attribute defaults to 300, and the height attribute defaults to 150.