---
title: "Quick rack space and weight sizing calculator for homelab and small data center racks. Enter your devices with their height in rack units, weight, and wattage to get total utilization, remaining free space, weight totals in lbs and kg, and recommended PDU count based on the NEC 80% continuous load rule (1920W per 20A/120V PDU). Estimates cable management overhead at 2U per 10U of installed gear. Outputs total_watts that chains into power_cost and cooling_btu for full infrastructure planning."
method: POST
path: "/api/rack_capacity"
tags: ["homelab"]
---

# Quick rack space and weight sizing calculator for homelab and small data center racks. Enter your devices with their height in rack units, weight, and wattage to get total utilization, remaining free space, weight totals in lbs and kg, and recommended PDU count based on the NEC 80% continuous load rule (1920W per 20A/120V PDU). Estimates cable management overhead at 2U per 10U of installed gear. Outputs total_watts that chains into power_cost and cooling_btu for full infrastructure planning.

`POST /api/rack_capacity`

## Request

- Base URL: `https://calc.engineer`
- URL: `https://calc.engineer/api/rack_capacity`
- Auth: none declared

## Request body

- object
  - `rack_units` number: Total rack height in rack units (standard is 42U)
  - `devices` object[], required: List of devices to place in the rack
    - `name` string: Optional label for the device (e.g. 'Dell R730', 'Patch Panel')
    - `height_u` number, required: Height of the device in rack units (U)
    - `weight_lbs` number: Weight of the device in pounds
    - `watts` number: Power draw of the device in watts

## Response `200`

Computed result for rack_capacity

- object
  - `result` object, required
    - `used_u` number, required: Total rack units consumed by devices
    - `free_u` number, required: Remaining empty rack units
    - `utilization_pct` number, required: Percentage of rack space used by devices
    - `total_weight_lbs` number, required: Total weight of all devices in pounds
    - `total_weight_kg` number, required: Total weight of all devices in kilograms
    - `total_watts` number, required: Total power draw of all devices in watts
    - `recommended_pdu_count` number, required: Recommended number of PDUs (each PDU = 80% of 20A/120V = 1920W)
    - `overhead_u` number, required: Estimated cable management overhead in rack units (2U per 10U of gear)
    - `effective_free_u` number, required: Free rack units after subtracting cable management overhead
  - `tool` string, required
  - `version` string, required
  - `computed_at` string, date-time, required
  - `chain` object, required
    - `feeds` unknown[]
      - unknown
    - `accepts_from` unknown[]
      - unknown

## Other responses

- `400`: Validation error or invalid JSON
- `404`: Tool not found

---

[API](https://skmtc.dev/calc/apis/calc-engineer-api.md) · [All operations](https://skmtc.dev/calc/apis/calc-engineer-api/llms.txt) · [OpenAPI document](https://skmtc.dev/calc/apis/calc-engineer-api/revisions/8830480ec488?raw)