Simple Math

You'll often need simple arithmetic, like cleanly halving an image size or adjusting the batch size. Let's look at the nodes for that.

I used to install a custom node for this, but core now has a node that does the same thing, so it's no longer needed.

Math Expression

math_expression.json

You can put a number into each of a, b, and c. Then write something like a * b - c with those variables to do basic arithmetic.

And since it takes Python expressions as-is, you can do somewhat more advanced math too.

a // b       # Integer division (truncate decimal places)
a % b        # Modulo (remainder of division)
a ** b       # Exponentiation (power)
(a + b) * c  # Specify priority with parentheses

abs(a - b)   # Find absolute value
min(a, b)    # Return minimum value
max(a, b)    # Return maximum value
round(a / b) # Round off

(a > b) * 1  # Logic expression: Convert condition to number (1 if a > b, otherwise 0)
(a == b) * 1 # Logic expression: Determine if equal
(a != b) * 1 # Logic expression: Determine if different

int and float

Numbers have types. ComfyUI mainly uses two: int and float.

  • int type: Integers only (e.g., 512, 32, 1)
    • Batch size, image resolution, etc.
  • float type: Can handle decimals (e.g., 0.7, 1.5, 24.0)
    • KSampler strength, video fps, etc.

You can't connect nodes unless the types match. I can already hear someone saying "Why not just make everything a float?", but they're kept separate for efficiency and precision... you'll just have to get used to it.

Type Conversion

By the way, passing a value through a Math Expression node lets you convert between int ↔ float.

Even if the input is a float, it's converted automatically when the destination expects an int.

math_expression_floatint.json

[Tip] Quick Math in Input Fields

For simple math that isn't worth a node, type the expression straight into an input field and it fills in the result.

Power Puter (rgthree)

With Power Puter from rgthree-comfy, you can do more complex things, like getting an image's size or using if statements. At that point it's pretty much programming.

cf. Node: Power Puter (Wiki)

power_puter.json