# Creates a unit of measure group.

`POST /inventory/unit-of-measure-groups`

Group: Inventory › Unit of Measure Groups · Operation ID: `createUnitOfMeasureGroup`

The response is only the created unit of measure group's id. Read the group with GET inventory/unit-of-measure-groups/:id when you need its stored state, including the ids assigned to its lines. The base unit gets its own line automatically with a factor of 1, so send baseUnitOfMeasureId and leave it out of lines. Each unit of measure may appear at most once in the group. Use POST inventory/unit-of-measure-groups/bulk to create several at once.

[Open in the interactive reference](https://docs.api.lensing.ai/?op=createUnitOfMeasureGroup)

## Parameters

| Name | In | Type | Required | Description |
| --- | --- | --- | --- | --- |
| `Api-Version` | header | `"v1"` | yes | The API version this request targets, named by its public identifier. Required on every request; omitting it, or naming a version this company does not have, is answered with 400. This document describes version `v1`. |
| `Idempotency-Key` | header | string | no | An opaque caller-chosen string (1-255 characters) that makes this request safe to retry. Repeating the same key with an identical request body replays the original response instead of re-executing - but only once that original request succeeded; a failed attempt re-executes on retry. Repeating the key with a different body is answered with 422. A key still in flight is answered with 409 - as is a key whose original request was interrupted before it finished, for a few minutes afterwards, until that attempt is presumed dead. A completed response stays replayable for 24 hours. The key is scoped to the caller, not to the action: reusing it for a different action is answered with 409 or 422 rather than treated independently. On read actions this header is ignored. On write actions that cannot offer the guarantee it is answered with `400 IDEMPOTENCY_NOT_SUPPORTED` rather than silently ignored. |

## Request body

Required, `application/json`: createUnitOfMeasureGroupInput.

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `name` | string | yes | The display name of the unit of measure group. Required. It is not checked for uniqueness. |
| `description` | string | no | A free-form description of what the group covers. Omit for none. |
| `baseUnitOfMeasureId` | string | yes | The unique identifier for the base unit of measure that every conversion factor in the group is relative to. Required. It is fixed for the life of the group and gets its own line automatically with a factor of 1, so do not list it in lines. See id on GET inventory/unit-of-measures/:id. |
| `lines` | array of object | no | The conversion lines to add, beyond the base unit's automatic one. Omit for a group with only its base unit. Each unit of measure may appear at most once, and none may be the base unit. |
| `lines[].unitOfMeasureId` | string | yes | The unique identifier for the unit of measure this line converts. It must not be the base unit and must not repeat another line in this request. See id on GET inventory/unit-of-measures/:id. |
| `lines[].conversionFactor` | string (decimal) | yes | How many base units of measure make up one of this unit. It must be greater than zero. |

Example:

```json
{
  "name": "Packaging",
  "description": "Eaches, boxes and pallets",
  "baseUnitOfMeasureId": "3b7d5e9c-1a24-4f80-9c6d-2e8f70b13a45",
  "lines": [
    {
      "unitOfMeasureId": "8c1f4a72-6b09-4d15-a3e7-40d2b6915cf8",
      "conversionFactor": "12.00"
    }
  ]
}
```

## Response

`200` Success

Under `data` (createUnitOfMeasureGroupOutput):

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `id` | string | yes | The unique identifier for the created unit of measure group. |

## Response headers

- `Idempotency-Replayed` — Present and `true` only when this response replays a previously stored one for the same Idempotency-Key, rather than reflecting a live execution. Absent on a live response - never sent as `false`.

## Errors

| Code | Status |
| --- | --- |
| `UNIT_NOT_FOUND` | 400 |
| `DUPLICATE_UNIT_IN_GROUP` | 400 |
| `INVALID_CONVERSION_FACTOR` | 400 |
| `IDEMPOTENCY_KEY_CONFLICT` | 409 |
| `IDEMPOTENCY_PAYLOAD_MISMATCH` | 422 |

## Statuses

- `400` — Invalid request or business failure. Codes: UNIT_NOT_FOUND, DUPLICATE_UNIT_IN_GROUP, INVALID_CONVERSION_FACTOR
- `401` — Missing or invalid access token
- `403` — Not authorized
- `404` — Not found
- `409` — The Idempotency-Key is still being processed by another request.
- `422` — The Idempotency-Key was already used with a different request payload.
- `429` — Too many requests
- `500` — Internal server error