Turbine blade, set of turbine blades, and fir tree root for a turbine blade

A turbine blade having an airfoil and a fir tree root is disclosed. The fir tree root has a lengthwise direction, a crosswise direction extending between two lateral sides of the fir tree root, and a span direction extending from a root base towards an airfoil tip. The fir tree root includes a web interposed between each pair of at least two neighboring channels. For each web, a web-to-channel ratio with each of the two neighboring channels is chosen to be larger than or equal to 0.5 and is smaller than or equal to 0.85 at least at a position where the root width is a minimum load bearing root width in a load bearing section of the fir tree root. In another aspect, overall web-to-channel ratio is defined as a ratio between the sum of all web lengths and the sum of all channel lengths.