sqrt

sqrt returns the square root of a non-negative number - the value that, multiplied by itself, gives you the input. It's a one-input, one-output node from the Basic data handling pack, and it shows up in ComfyUI workflows more than you'd expect, because several practical formulas are built on roots.

The classic one: scaling by area instead of side. If a value represents area (pixels, tile count, coverage), its square root is the linear dimension - so when you want a size knob that feels linear but the underlying math is quadratic, sqrt is the fix. Similarly, RMS-style averaging (root of the mean of squares) is a sqrt, and easing curves often use sqrt or pow(x, 0.5) as the "fast-out, slow-in" shape.

How it works

A wrapper around Python's math.sqrt(). One input, one output:

• value - FLOAT or INT, default 0. The UI enforces a minimum of 0.
• FLOAT output - the square root.

Sanity anchors: sqrt(0) = 0, sqrt(1) = 1, sqrt(4) = 2, sqrt(2) ≈ 1.414. Fractions work fine - sqrt(0.25) = 0.5.

The domain rule

You cannot take the square root of a negative number (in real-number math). Python will raise a math domain error, and unlike the input widget's min, a wired-in value that drifts negative will trigger it at runtime. If your input can go below zero, clamp it first - max(value, 0) from the pack's max node, or an epsilon if you need to avoid exact zero. That single troubleshooting step covers 100% of the errors this node can throw.

When you'd grab it

• Perceptually linear sliders for quadratic quantities (areas, resolutions, sizes).
• RMS / averaging math where you want a root-mean-square value.
• Inverse of ** 2 - if a formula squares something upstream, sqrt is how you undo it cleanly.

It also pairs naturally with the pack's MathFormula node if you want to combine it with other math in one expression - sqrt(a) is a supported function call there.

Installing it

The whole pack is dependency-free - no models, no pip requirements, nothing to download past the clone. ComfyUI Manager, search "Basic data handling", install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/StableLlama/ComfyUI-basic_data_handling

Restart, and sqrt sits under Basic/maths next to exp and log.

Bottom line

sqrt isn't a node you'll place every day, but the day you're wrestling a quadratic relationship it's the difference between a formula and a guess. Cheap, correct, and it fails loudly (with a clear error) instead of silently - which is all you can ask of a math node.