Unit Conversion Rules of Thumb

Question 1

Feet to Metres or vice versa.

Answer 1

1 foot is about 30cm. (ft / 3) - 10% = metres.

1 metre is about 3.3 ft. (m X 3) + 10% = feet.

Question 2

Nautical Miles to Kilometers, or vice versa.

Answer 2

1NM is 1.85km. (NM X 2) - 10% = kilometers.

1km is 0.54NM. (km / 2) + 10% = nautical miles.

Question 3

NM and Kilometers to Feet.

Answer 3

1NM is about 6000ft.

1km is about 3300ft.

Question 4

Knots to Kilometres per Hour, or vice versa.

Answer 4

(kt X 2) - 10% = kilometres per hour.

(km/h / 2) +10% = knots.

Question 5

Metres per Second to Feet per Minute, or vice versa.

Answer 5

m/s X 200 = feet per minute.

ft/minute / 200 = metres/second.

Question 6

Litres to US Gallons, or vice versa.

Answer 6

(litre / 4) + 5% = US Gal

(US Gal X 4) - 5% = litres.

Question 7

Pounds to Kilograms, or vice versa.

Answer 7

(kg X 2) + 10% = pounds.

(lb / 2) - 10% = kilograms.

Question 8

Indicated Air Speed to True Air Speed, or vice versa.

Answer 8

True air speed is about 2% higher than IAS per 1000ft of altitude.

Question 9

True Air Speed to Mach Number, or vice versa.

Answer 9

True airspeed / 600kt = Mach number

Question 10

Knots to Meters per Second

Answer 10

Knots / 2 = meters per second

Question 11

Knots to Feet per Minute

Answer 11

Knots X 100 = feet/minute

Question 12

Ground speed to Rate of Descent (assuming a 3 degree gradient)

Answer 12

Ground speed in Knots X 5 = rate of descent in feet/minute

Question 13

Rate of deceleration of aircraft in flight

Answer 13

10kt per 1NM

Question 14

How far away to begin descent based on height

Answer 14

(Flight level / 10) X 3 = distance of descent in NM