The metric system or the International System of Units, is rapidly becoming the Australian system of measurement. To avoid complicated conversions from "old" measures to new, it is easier to THINK METRIC all the time. Buy a good set of metric measuring tools and order, work and think only in metric measurements. This system gives us the metre for length, the square metre for area, and the cubic metre for volume. Larger and smaller units are obtained by combining set prefixes within the basic unit. For example, milli means a thousandth (as in millimetre); kilo means a thousand times (as in kilometre).

The handyman.
The sizes of most tools have not changed but descriptions may have. Hammers, saws and shovels, chisels and paint brushes for example, are still the same general sizes but, for instance a 4 inch brush (10.16 cm) may be referred to as a 10 centimetre brush.
In nuts and bolts, we no longer use the inch-based screw threads. Whitworth, S.A.E. and B.S.F. You will need to purchase a metric set of socket spanners, drills, tap and die sets etc where thread in nut, bolt and tool must match.

Ordering materials.
Timber sizes for green off-saw hardwood convert on the basis of 1 inch to 25 millimetres so the well known 4 x 2 has become 100 x 50mm. Softwood is also in millimetres indicating the minimum dry finishes sizes. Timber is sold by the metre and cubic metre.
Bricks are now in metric sizes. Their nominal dimensions are 230 x 110 x 76mm. With a 1Omm. mortar joint they can be laid so that 7 courses are 60Omm for modern modular metric building They can also be used for renovating existing brickwork because they are close enough in size to imperial sized bricks.
Cement and concrete are sold by the 40kg giving 25 bags to the tonne.
Ready-mixed concrete is sold in cubic metres.
Paint is sold in millilitres such as 250ml, 500ml, 1, 4 and 10 litres.
Glass is specified in millimetres of thickness. Length and breadth are described in millimetres and glass is sold by the square metre.
While you should try to THINK METRIC every way possible, the chart will guide you in the relative values of imperial and metric measurements.