Units

Length: 1 m = 10⁶ µ m = 10⁹ nm = 10¹⁰ Å

Volume:
●   Cubic Meter (cube of 1m side)  = 1 m³
■   1 m³  = 1,000 dm³ (cubic decimeter) = 1,000,000 cm³ (cubic centimeter) = 1,000,000,000 mm³ (cubic millimeter) 
●   Liter : 1 L = 1 dm³
■   1 L = 10 dL (deciliter) = 100 cL (centiliter) = 1,000 mL (milliliter) = 1,000 cm³ = 1,000,000 µL (microliter).
E.g. The volume of a drop is about 50 µL.

Weight:
●   Kilogram (kg): 
  ■  1 kg = 1,000 g (grams) = 1,000,000 mg (milligram) = 1,000,000,000 µg (microgram).
●   Ton : 1 Ton = 1,000 kg
●   Water density : dwater = 1═> 1 L = 1 kgConcentration:
■   ppm = 1 part per million (= 1/1,000,000)
■   ppb =  1 part per billion  (= 1/1,000,000,000)
■   ppt = 1 part per trillion  (= 1/1,000,000,000,000)
■   ppq = 1 part per quadrillion (1/1,000,000,000,000,000)

 On a weight scale :
◆  1 ppm = 1mg / kg
 ◆  1 ppb = 1 µg / kg 
◆  1 ppt = 1 ng / kg

 On a time scale :
◆  1 ppm = 1 second per 11.5 days
◆  1 ppb = 1 second per 32 years
◆  1 ppt =1 second per 320 centuries