2x4 = 38x89mm
2x6 = 38x140mm
2x8 = 38x184mm
2x10 = 38x235mm
2x12 = 38x286mm
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1x2=3/4" x 1 1/2" =19mm x 38mm
1x3=3/4" x 2 1/2" =19mm x 64mm
1x4=3/4" x 3 1/2" =19mm x 89mm
1x5=3/4" x 4 1/2" =19mm x 114mm
1x6=3/4" x 5 1/2" =19mm x 140mm
1x7=3/4" x 6 1/4" =19mm x 159mm
1x8=3/4" x 7 1/4" =19mm x 184mm
1x10=3/4" x 9 1/4"=19mm x 235mm
1x12=3/4" x 11 1/4"=19mm x 286mm
1 1/4x4= 1" x 3 1/2"=25mm x 89mm
1 1/4x6=1" x 5 1/2"=25mmx140mm
1 1/4x8=1" x 7 1/4"=25mm x 184mm
1 1/4x10=1" x 9 1/4"=25mm x 235mm
1 1/4x12=1" x 11 1/4"=25mm x 286mm
1 1/2x4=1 1/4" x 3 1/2"=32mm x 89mm
1 1/2x6=1 1/4" x 5 1/2"=32mm x 140mm
1 1/2x8=1 1/4" x 7 1/4"=32mm x 184mm
1 1/2x10=1 1/4" x 9 1/4"=32mm x 235mm
1 1/2x12=1/1/4" x 11 1/4"=32mm x 286mm
2x4=1 1/2" x 3 1/2"=38mm x 89mm
2x6= 1 1/2" x 5 1/2"=38mm x 140mm
2x8=1 1/2" x 7 1/4"=38mm x 184mm
2x10=1 1/2" x 9 1/4"=38mm x 235mm
2x12=1 1/2" x 11 1/4"=38mm x 286mm
3x6=2 1/2" x 5 1/2" =64mm x 140mm
4x4=3 1/2" x 3 1/2"=89mm x 89mm
4x6=3 1/3" x 5 1/2"=89mm x 140mm
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1x4 = 19mm x 90mm
1x5 = 19mm x 120mm
1x6 = 19mm x 140mm
1x8 = 19mm x 190mm
1x10 = 19mm x 240mm

2x4 = 35mm x 90mm
2x5 = 35mm x 120mm
2x6 = 35mm x 140mm
2x8 = 35mm x 190mm
2x10 = 35mm x 240mm
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http://www.ana-white.com/2010/09/timber-lumber-sizes-metric-compared-against-dimensional