How to Find the Maximum of Three Numbers in Python

To find the maximum of three numbers in Python, call the built-in max() with all three values: max(a, b, c) returns the largest one. Wrap it in a function if you need it more than once:

def largest_of_three(a, b, c):
    return max(a, b, c)

Every program below was run on Python 3.12.5 in Command Prompt, and the outputs shown are copied from those runs.

You’ll see max(), the classic if-elif-else program (plus a tie bug most copies have) and numbers typed by a user.

Find the maximum of three numbers with max()

max() takes any number of arguments and returns the biggest, including negatives and int/float mixes:

def largest_of_three(a, b, c):
    return max(a, b, c)

austin, denver, boston = 18450.75, 21309.40, 19876.00
print(f"Highest weekly sales: ${largest_of_three(austin, denver, boston):,.2f}")
print(largest_of_three(-4, -9, -1))
print(largest_of_three(2, 2.5, 2))      # int and float mix fine

Output:

Highest weekly sales: $21,309.40
-1
2.5

For numbers already in a list, see finding the largest number in a list covers that, and the max() function in depth explains key and default.

Find the greatest of three numbers using if-elif-else

Homework often says “don’t use max()”. The version most tutorials print uses strict >, and it breaks when two numbers tie for the top:

def greatest_strict(a, b, c):           # common version with a hidden bug
    if a > b and a > c:
        return a
    elif b > a and b > c:
        return b
    else:
        return c

def greatest(a, b, c):                  # >= handles ties
    if a >= b and a >= c:
        return a
    elif b >= c:
        return b
    else:
        return c

for nums in [(12, 7, 3), (4, 15, 9), (9, 9, 5)]:
    print(nums, "strict:", greatest_strict(*nums), " fixed:", greatest(*nums))

Output:

(12, 7, 3) strict: 12  fixed: 12
(4, 15, 9) strict: 15  fixed: 15
(9, 9, 5) strict: 5  fixed: 9

With >=, the first branch wins any tie, and the elif only needs to compare b and c. If and or elif are new to you, see if-else in Python and logical operators in Python.

Can you find the largest of three numbers in one line?

Yes, with a conditional expression (Python’s ternary). A short loop or sorted() also skips max():

a, b, c = 48, 91, 77
biggest = a if a >= b and a >= c else (b if b >= c else c)
print("Ternary:", biggest)

biggest = a
for n in (b, c):                        # no max() and no elif chain
    if n > biggest:
        biggest = n
print("Loop:   ", biggest)
print("Sorted: ", sorted([a, b, c])[-1])

Output:

Ternary: 91
Loop:    91
Sorted:  91

Nested ternaries get hard to read, so I keep them short. The loop is the idea behind finding the largest and smallest numbers in longer data, and sorting is covered in sorting a list without sort().

Take three numbers from user input

input() always returns a string, and strings are compared character by character. So "9" beats "10" because "9" comes after "1". Convert first:

a = input("First number: ")
b = input("Second number: ")
c = input("Third number: ")
print("As strings:", max(a, b, c))      # text comparison, character by character

try:
    nums = [float(x) for x in (a, b, c)]
    print("As numbers:", max(nums))
except ValueError:
    print("Please enter numbers only.")

Output:

First number: 9
Second number: 10
Third number: 4
As strings: 9
As numbers: 10.0

float() accepts decimals, and the except catches bad typing. See asking for user input in Python and on checks in checking if input is a number.

Want more beginner programs like this one? Try these:

• Find the product of three numbers in Python
• Swap two numbers in Python
• Check if a number is even or odd
• Define a function in Python

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