Thought I'd give /u/Enjgine'd code a second refactoring - https://redd.it/avnpue

second.py

import os


def cls():
    os.system('cls' if os.name == 'nt' else clear)


# this is a function that returns a dictionary/key-value-pair 'list'
# the reason that this isn't a regular variable, as that they can be changed
# and Python doesn't have any constants, so you can use a function that returns
# a value to emulate constants.
# you could transform this to a lambda (once you know what that is and, more
# importantly, what it's for), but that's just a style choice
def units():
    return {
        'cm': 1,
        'm': 100,
        'inch': 2.54,
        'foot': 30.48
    }


# you could make this and units() a two-liner if you want, but this is a bit
# more readable, IMO
def targets():
    return {
        'cm': 1,
        'm': 100,
        'inch': 2.54,
        'foot': 30.48
    }


while True:
    mode = input('Enter starting unit (cm,m,inch,foot): ')
    # moved float() to adhere to DRY - Don't Repeat Yourself :)
    distance = float(input('Enter the length you wish to convert: '))
    target = input('Enter your target unit (cm,m,inch,foot): ')

    # get the value to convert the distance to centimeters
    distance *= units().get(mode)
    # get the value to convert distance to its target
    distance /= targets().get(target)
    # print the converted value
    print(distance, target)

    # no need for the wait variable, as it's not in use
    input("Press enter to continue.")
    cls()
    pass