### Common units

Kilometer (km), meter (m), centimeter (cm), millimeter (mm), mile (mi), feet (ft), inch (in)

1 km = 1,000 m = 0.62 mi

1 m = 100 cm = 1,000 mm = 3.28 ft = 39.37 in

1 in = 25.4 mm

1 mi = 5,280 ft
Square meter (m²), square feet (ft²)

1 m² = 10.76 ft²

10 ft² = 0.93 m²
Cubic meter (m³), liter (L), milliliter (mL), cubic centimeter (cc), gallon (gal), quart (qt), pint (pt), ounce (fl oz), cubic feet (ft³)

1 m³ = 1,000L = 264.2gal

1 L = 1,000mL = 1,000cc = 0.2642gal

1 gal = 4qt = 8pt = 128fl oz = 0.134ft³ = 3.785L

1 ft³ = 7.48gal = 28.3L
Metric ton (t), kilogram (kg), gram (g), ton (tn), pound (lb), ounce (oz)

1 t = 1,000 kg = 1.1 tn

1 kg = 1,000 g = 2.2 lb

1 tn = 2,000 lb

1 lb = 16 oz
Celsius (°C), kelvin (K), fahrenheit (°F)

°F = °C × 9/5 + 32

K = °C + 293.15
kilogram / cubic meter (kg/m³), g / cubic centimeter (g/cm³), pound / cubic feet (lb/ft³), pound / gallon (lb/gal)

1,000kg/m³ = 1g/cm³ = 62.43lb/ft³ = 8.35lb/gal
Specific gravity (S.G.) is ratio of density between specific matter and water. So, specific gravity is dimensionless
Kilometer / hour (km/hr), meter / minute (m/min), meter / second (m/s), mile / hour (mi/hr), foot / minute (ft/min), foot / second (ft/s)

3.6km/hr = 60m/min = 1m/s = 3.28ft/s

0.68mi/hr = 60ft/min = 1ft/s
Cubic meter / hour (m³/hr), liter / minute (Lpm), liter / second (L/s), Cubic meter / second (m³/s), gallon / minute (gpm)

3.6 m³/hr = 60 Lpm = 0.001 m³/s = 1L/s = 15.85 gpm

1 gpm = 0.063 L/s = 3.785 L/min = 0.227 m³/hr
Newton (N), kilonewton (kN), pound force (lbf)

1 kN = 1,000 N = 224.8 lbf
Kilowatt hour (kW·h), joule (J), British thermal unit (BTU), calorie (cal)

1 kW·h = 3,600,000 J = 3,412.14 BTU = 859.85 cal
Kilowatt (kW), watt (W), horse power (hp)

0.746 kW = 746 W = 1 hp
Newton meter (N·m), pound force foot (lbf·ft)

1 N·m = 0.74 lbf·ft

1 lbf·ft = 1.36 N·m
Revolution / minute (rpm), revolution / second (rev/s) radian / second (rad/s)

60 rpm = 1 rev/s = 6.28 rad/s
Pascal (Pa), kilopascal (kPa), megapascal (MPa), bar, kilogram / square centimeter (kgf/cm²), atmosphere (atm), pound / square inch (psi)

1 MPa = 1,000 kPa = 1,000,000 Pa = 10 bar = 10.2 kgf/cm² = 145 psi

1 atm = 1.0133 bar = 14.7 psi
Kilogram meter square (kg·m²), gram centimeter square (g·cm²), pound foot square (lb·ft²)

1 kg·m² = 10,000,000 g·cm² = 23.73 lb·ft²
Concentration units are classified as 4 main types

- Volume against volume (v/v) - percentage (%), part per thousand (ppt), part per million (ppm)

- Mass against mass (w/w) - percentage (%), part per thousand (ppt), part per million (ppm)

- Mass against volume (w/v) - kilogram / cubic meter (kg/m³), gram / 100 milliliter (g/100mL); 1 kg/m³ = 0.1 g/100mL

- Molar concentration (Molarity) - Mole / liter (c or mol/L); 1 c = 1 mol/L

These 4 types of concentration units are only interchangeable under certain condition
N·s/m², Pa·s, mPa·s, poise (P), centipoise (cP, cp, cPs)

1 N·s/m² = 1 Pa·s = 1,000 Pa·s = 10 P = 1,000 cP
m²/s, mm²/s, stoke (St), centistoke (cSt)

0.0001 m²/s = 100 mm²/s = 1 St = 100 cSt
Kinematic viscosity (m²/s) = Dynamic viscosity (N·s/m²) / Density (kg/m³)
There are many other viscosity units, such as SSU, SUS, SSF.

However, most of them replaced by either dynamic viscosity units or kinematic viscosity units as their conversion are usually under limitations.
﻿