The ratio is not a specific measure but rather a general indication of a force's might in relation to the resources it devotes to supply, upkeep, and logistics.
It may be measured for an entire national military, a single branch, a theater of operations, or down to individual formations.
Tooth-to-tail ratio is often inversely related to its technological capabilities and subsequently its overall power.
While a force with a high tooth-to-tail ratio will have more personnel devoted to combat, these soldiers will lack the support provided by the tail.
Such support includes the logistics and communication infrastructure on which modern forces depend.