Question 1

How do I convert PSI to bar or kPa?

Accepted Answer

1 PSI = 6.8948 kPa = 0.068948 bar. To convert: kPa = PSI × 6.8948. Bar = PSI × 0.068948. For quick mental calculations: 100 PSI ≈ 6.9 bar ≈ 690 kPa. This is used in South African industry where hydraulic systems often specify pressures in PSI (imported equipment) while SA standards (SANS) and gauges use bar or kPa.

Question 2

How do I convert between kW and horsepower (hp)?

Accepted Answer

1 hp (mechanical) = 0.7457 kW. 1 kW = 1.341 hp. For motors: A 37 kW motor is approximately 49.6 hp. Note: There are three types of horsepower — mechanical (745.7 W), metric/PS (735.5 W common in Europe), and electrical (746 W). Metric HP (PS/CV) is very close but slightly less than mechanical HP. In South Africa, motors are rated in kW (SI), not hp.

Question 3

How do I convert °C to °F and vice versa?

Accepted Answer

Celsius to Fahrenheit: °F = (°C × 9/5) + 32. Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Key reference points: 0°C = 32°F (water freezes), 100°C = 212°F (water boils), 37°C = 98.6°F (body temperature), −40°C = −40°F (crossover point). For Kelvin: K = °C + 273.15.

Question 4

What is the difference between mass and weight?

Accepted Answer

Mass (kg) is the amount of matter in an object — constant everywhere in the universe. Weight is the gravitational force on that mass: W = m × g (Newtons). At sea level on Earth (g = 9.81 m/s²): 1 kg = 9.81 N weight. In everyday use, we say "weight" in kg which is really mass. In engineering: Load in N = mass (kg) × 9.81. South African standard: SANS uses SI units — kg for mass, N for force.

Question 5

How do I convert litres per minute (L/min) to m³/h?

Accepted Answer

L/min to m³/h: Multiply by 0.06. Example: 500 L/min × 0.06 = 30 m³/h. L/min to m³/s: Multiply by 1/60,000 = 0.000016667. L/min to GPM (US): Multiply by 0.26417. This conversion is common for pump flow rates. South African water and mining pumps typically spec in L/s or m³/h; imported pumps often use GPM.

Question 6

How do I convert N·m (Newton-metres) to ft·lbf?

Accepted Answer

1 N·m = 0.7376 ft·lbf. 1 ft·lbf = 1.3558 N·m. For torque wrenches: 100 N·m = 73.76 ft·lbf. This matters for tightening fasteners — imported service manuals (especially mining and automotive) cite ft·lbf or in·lbf while SANS fastener standards use N·m. Tip: A 100 N·m ≈ 74 ft·lbf (easy mental shortcut).

Question 7

What is the conversion between kWh and MJ (energy)?

Accepted Answer

1 kWh = 3.6 MJ = 3,600 kJ. 1 MJ = 0.2778 kWh. Practically useful for energy management under SANS 50010 (energy management) and Eskom billing. If a pump uses 37 kW and runs 8 hours: Energy = 37 × 8 = 296 kWh = 1,065.6 MJ. At R2.50/kWh: Cost = R740/day. BTU to kWh: 1 BTU = 0.000293 kWh. 1 kWh = 3412 BTU.

Question 8

How do I convert between bar and metres of water column (mWC)?

Accepted Answer

1 bar = 10.197 mWC (metres of water column). 1 mWC = 0.0981 bar = 9.81 kPa. This is essential for pump head calculations: Pump head (m) = Pressure (kPa) / (ρ × g) = kPa / 9.81 (for water at ~1000 kg/m³). Example: A pump delivers 3.5 bar = 35.7 mWC total head. Used extensively in South African water reticulation and fire protection (SANS 10090) specifications.

Unit	Value	Symbol / Name
Millimetre (mm)	1000	Click to set as target
Centimetre (cm)	100	Click to set as target
Metre (m)	1	← current source
Kilometre (km)	0.001	Click to set as target
Inch (in)	39.370079	Click to set as target
Foot (ft)	3.2808399	Click to set as target
Yard (yd)	1.0936133	Click to set as target
Mile (mi)	0.00062137119	Click to set as target
Nautical Mile (nmi)	0.0005399568	Click to set as target
Micrometre / Micron (µm)	1000000	Click to set as target

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