Question 1

How many millimetres are in an inch?

Accepted Answer

Exactly 25.4 mm. Since 1959 the inch has been defined as 25.4 mm, so 1/16 in is 1.5875 mm and 1 ft is 304.8 mm.

Question 2

How do I convert millimetres to inch fractions?

Accepted Answer

Divide by 25.4 to get decimal inches, then multiply the decimal part by 16 (or 32, 64) and round. 100 mm is 3.937 in, which is 3 15/16 in to the nearest sixteenth, 0.0125 mm more than the exact value.

Question 3

Is a 2440 × 1220 mm sheet the same as 8 × 4 ft?

Accepted Answer

Almost. 8 × 4 ft is 2438.4 × 1219.2 mm, so a European 2440 × 1220 sheet is 1.6 mm longer and 0.8 mm wider. Plan your parts with the cut list for sheets.

Question 4

What is the difference between a US and a UK gallon?

Accepted Answer

A US gallon is 3.785 L and a UK (imperial) gallon is 4.546 L, about 20% more. Pints and fluid ounces differ too: a US pint is 473 mL and a UK pint 568 mL; a US fl oz is 29.57 mL and a UK fl oz 28.41 mL.

Question 5

How many psi is 1 bar?

Accepted Answer

1 bar is 14.504 psi, and 1 psi is 0.0689 bar. A tyre at 2.5 bar is at about 36 psi.

Question 6

Can a unit mix-up be dangerous?

Accepted Answer

Yes. A torque in lbf·in instead of lbf·ft is 12 times too low, a bar/psi mix-up is a factor of 14.5, kg and lb differ by a factor of 2.2, and 180 °F is only 82 °C. Check the unit on the gauge or label, and keep the original value next to the converted one.