To convert Meters to feet in your head: multiply [meters] times three; add 10% of the total *to* the total.
Example: 1000 meters X 3 = 3000
10% of 3000 = 300
sum = 3300ft


Example#2: 2,500m X3 = 7500, +750 (because 750 is 10% of 7,500) = 8250ft



Altitude

500m = 1,500'
1,000m = 3,300'
2,500m = 8,300'
5,000m = 17,000'
9,000m = 30,000'
10,000m = 33,000'


Speed (rounded)

100km = 63mi (that's statute miles, not nautical)
200km = 125mi
250km = 160mi
400km = 250mi
500km = 320mi
800km = 500mi
1000km = 630mi.