---
title: "union"
subtitle: "Function in std::solid"
excerpt: "Union two or more solids into a single solid."
layout: manual
---

Union two or more solids into a single solid.

```kcl
union(
  @solids: [Solid],
  tolerance?: number,
): [Solid]
```



### Arguments

| Name | Type | Description | Required |
|----------|------|-------------|----------|
| `solids` | [`[Solid]`](/docs/kcl-std/types/std-types-Solid) | The solids to union. | Yes |
| `tolerance` | [`number`](/docs/kcl-std/types/std-types-number) | The tolerance to use for the union operation. | No |

### Returns

[`[Solid]`](/docs/kcl-std/types/std-types-Solid)


### Examples

```kcl
// Union two cubes using the stdlib functions.


fn cube(center, size) {
  return startSketchOn(XY)
    |> startProfile(at = [center[0] - size, center[1] - size])
    |> line(endAbsolute = [center[0] + size, center[1] - size])
    |> line(endAbsolute = [center[0] + size, center[1] + size])
    |> line(endAbsolute = [center[0] - size, center[1] + size])
    |> close()
    |> extrude(length = 10)
}

part001 = cube(center = [0, 0], size = 10)
part002 = cube(center = [7, 3], size = 5)
  |> translate(z = 1)

unionedPart = union([part001, part002])
```

![Rendered example of union 0](data:image/png;base64,[encoded data, 83132 characters])

```kcl
// Union two cubes using operators.
// NOTE: This will not work when using codemods through the UI.
// Codemods will generate the stdlib function call instead.


fn cube(center, size) {
  return startSketchOn(XY)
    |> startProfile(at = [center[0] - size, center[1] - size])
    |> line(endAbsolute = [center[0] + size, center[1] - size])
    |> line(endAbsolute = [center[0] + size, center[1] + size])
    |> line(endAbsolute = [center[0] - size, center[1] + size])
    |> close()
    |> extrude(length = 10)
}

part001 = cube(center = [0, 0], size = 10)
part002 = cube(center = [7, 3], size = 5)
  |> translate(z = 1)

// This is the equivalent of: union([part001, part002])
unionedPart = part001 + part002
```

![Rendered example of union 1](data:image/png;base64,[encoded data, 83132 characters])

```kcl
// Union two cubes using the more programmer-friendly operator.
// NOTE: This will not work when using codemods through the UI.
// Codemods will generate the stdlib function call instead.


fn cube(center, size) {
  return startSketchOn(XY)
    |> startProfile(at = [center[0] - size, center[1] - size])
    |> line(endAbsolute = [center[0] + size, center[1] - size])
    |> line(endAbsolute = [center[0] + size, center[1] + size])
    |> line(endAbsolute = [center[0] - size, center[1] + size])
    |> close()
    |> extrude(length = 10)
}

part001 = cube(center = [0, 0], size = 10)
part002 = cube(center = [7, 3], size = 5)
  |> translate(z = 1)

  // This is the equivalent of: union([part001, part002])
  // Programmers will understand `|` as a union operation, but mechanical engineers
// will understand `+`, we made both work.
unionedPart = part001 | part002
```

![Rendered example of union 2](data:image/png;base64,[encoded data, 83132 characters])


