Speed, Force

Speed, force and pressure are measured differently by almost every industry that touches them. Aviation reports wind in knots, road signs use kilometres or miles per hour, and meteorologists often prefer metres per second. Tyre pressure appears in psi on an American gauge, in bar on a European compressor and in kilopascals on the label inside the door.

The mismatch is not academic. Inflating tyres to the psi figure when the specification was in bar leaves them dangerously soft, and misreading a torque figure between newton-metres and pound-feet damages fasteners. Engineers, mechanics, divers, pilots and sailors all move between these systems routinely and need conversions they can trust.

This converter handles the common speed, force and pressure units in one place, so a specification written for one market can be applied safely in another. Enter the value you have, choose the unit you need, and work from an exact figure rather than a remembered approximation.

How to use the Speed, Force

1. Choose whether you are converting speed, force or pressure.
2. Select the unit printed on your gauge, chart or specification.
3. Select the unit you need to work in.
4. Enter the value and read the converted figure.
5. Apply sensible rounding, especially for safety-critical settings such as tyre pressure.

Examples

• A driver converts a door-jamb tyre pressure of 220 kPa into psi to use a forecourt air line.
• A sailor converts a forecast of 25 knots into kilometres per hour before deciding to leave harbour.
• A mechanic converts a torque specification from newton-metres into pound-feet for an imperial torque wrench.

Frequently asked questions

How fast is one knot?

One knot is one nautical mile per hour, approximately 1.852 kilometres per hour or 1.151 miles per hour.

How do bar and psi relate?

One bar is about 14.5 psi, and it is very close to standard atmospheric pressure at sea level.

Is a kilogram a unit of force?

Strictly it is mass. The kilogram-force, still seen on older equipment, is the force gravity exerts on one kilogram, about 9.81 newtons.

Should I use gauge or absolute pressure?

Most everyday gauges read pressure above atmospheric, called gauge pressure. Scientific work often uses absolute pressure, which is about one bar higher.

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