ESDU 88033 is a guide to BS 436: Part 3: 1986 which provides a rigorous analytical procedure for rating a gear of known size in terms of allowable stresses or maximum power capacity. The method quantifies all the factors known to affect gear performance, and it requires a major reappraisal of traditional methods of gear design. ESDU 88033 discusses the factors, introduced in the new Standard, that affect material strength and the stresses induced, and provides advice on the choice of materials and manufacturing processes. An approximate method, compatible with BS 436: Part 3: 1986 enables the physical size of suitable gears to be determined from a known power transmission requirement. The method is summarised in a flowchart and illustrated by worked examples. A discussion of methods by which the new Standard may be used to generate gear design data for optimisation is included.