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Useful Measurements and Conversions


In the EU, measurements are normally given in metres and millimetres. This means that 54cm is written either as 0.54m or 540mm. 2m + 37.4cm is always 2.374m or 2374mm. Many DIY goods on sale in the UK will only list the metric measurement.

Linear Measurements

1 metre (1 m) is approximately 3ft 3in (39.37in).
1 inch when converted to metric, is 25.4mm.

However, when you go shopping, you will find that there is slight difference between the actual conversion and the manufacturers' conversion, so that items measuring 1 inch could be manufactured as 25mm. Because the manufacturer's conversion is always fractionally less than the actual conversion from imperial measurements, you should always measure in metric to avoid mistakes.

Imperial (inches)
Actual (mm) Manufacturers' Conversion (mm)
1 25.4 25
2 50.8 50
3 76.2 75
4 101.6 100
5 127 125
6 152.4 150
7 177.8 175
8 203.2 200
9 228.6 225
10 254.0 250
11 279.4 275
12 304.8 300
24 (2 ft) 609.6 600
36 (3 ft) 914.4 900
39 3/16in 1000.0 1000
48 (4 ft) 1219.2 1200
60 (5 ft) 1524.0 1500
72 (6 ft) 1828.8 1800
84 (7 ft) 2133.6 2100
96 (8 ft) 2438.4 2400

For example, if you want to buy a 6 ft long piece of timber you will find that the shops sell 1800mm or 1.8metre lengths.

If you continue to calculate using imperial measurements, you will have to convert them into metric measurements using the following conversion factors:

Imperial to metric Metric to Imperial
in x 25.4 = mm mm x 0.0394 = inch
ft x 0.3048 = metres mm x 0.0394 = inch
yd x 0.9144 = metres metres x 1.0936 = yard
Bricks and Blocks

The metric brick is slightly smaller than the old imperial one. It is posssible to bond metric bricks into old brick work by slightly increasing the mortar bed joint as shown in the table below.

  length width height typical joint
Metric 225mm 112.5mm 75mm 10mm
  8.86in 4.43in 2.95in 0.39in
Imperial 9in 41/2in 3in 3/8in
  228.6mm 114.3mm 76.2mm 9.5mm

Brick quantities

It takes 60 bricks to build 1 square metre of brick wall, the table below shows the number of bricks needed to build various sizes of wall.

Area Quantity
1m2 60 bricks
2m2 120 bricks
5m2 300 bricks
10m2 600 bricks

Building Blocks

One block covers the same area as 2 brick lengths and 3 brick heights. To cover the same size walls as the brick table above you will need :-

Area Quantity
1m2 10 blocks
2m2 21 blocks
5m2 53 blocks
10m2 106 blocks
Buying Timber

Timber can be purchased sawn, planed all round (PAR), or, planed both sides (PBS) (with the edges left sawn).

Sawn wood is very rough and is mostly used for structural work where the surface is not on show.

To make furniture or cupboards, you will need planed wood. Planing timber means that between 3mm and 5mm of wood is removed, so a 25mm piece of planed wood ends up as 22mm. A board measuring 152mm wide will end up as 146mm wide, as 3mm at each side will have been planed. You should note that when buying wood at timber yards or DIY stores, the sizes referred to are still sawn wood sizes — even after it has been planed to make it smooth. So a piece of 50 x 100mm PAR wood is actually 47 x 95mm.

When you buy timber, it's a good idea to try and buy the standard sizes as these are cheaper. Allow a little extra on lengths, in particular for cutting, and to compensate for any 'dirty' or damaged edges. A good rule of thumb is to add an extra 13mm for every 610mm.

Always reject wood with large knots as this is the sign of weak wood. Where there's a knot, there's often a bend or twist in the wood. End splits are another common fault and can sometimes extend right up the board. These are usually caused by rapid drying and you'll lose length because the split wood has to be cut away. Other defects to look out for are 'cupped' boards, where there is a warped curve across the width of the board.


Softwood comes in standard lengths of 1.80m (6 ft equivalent) 2.10m 2.40m 2.70m 3.0m 3.30m 3.60m 3.90m 4.20m 4.50m 4.80m 5.10m 5.40m 5.70m 6.0m and 6.30m

As stated above when buying planed softwood timbers, deduct 3mm from sawn sizes of the width and depth. For example, 25 x 50mm PAR (planed all round) is normally 22 x 47mm in actual size.


Plywood comes in sheets with thicknesses ranging from 3mm to 18mm.

Standard sheet sizes are : 2440 x 1220mm (8ft x 4ft), 1220 x 1220mm (4ft x 4ft) and 1220 x 610mm (4ft x 2ft). It is sometimes possible to have whole sheets cut to size by the timber yard (or DIY store), this can make using the sheets much easier and also makes it easier to get the sheets home if you are not having the boards delivered.

Chipboard also is sold in sheets with thicknesses of 9mm, 12mm, 15mm and 18mm. Standard sheet sizes for chipboard is 2440 x 1220mm (8ft x 4ft). Again it is someties possible to have the sheets cut to size by the timber yard.

Melamine and timber finished chipboard comes in a standard thickness of 15mm with plank lengths of 1820mm (6ft), 2440mm (8ft) and widths from 150mm (6in) to 600mm (2ft)

Hardboard is sold in sheets of 2440mm x 1200mm (8ft x 4ft) the thickness of standard hardboard is 3.2mm

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