---
title: "Estimates UPS (Uninterruptible Power Supply) backup runtime from battery specifications and connected load. Takes VA rating, watt rating, load in watts, and battery configuration (count, voltage, amp-hours) to compute effective stored energy after efficiency losses and runtime in minutes and hours. Detects overload conditions when load exceeds the UPS watt rating. Calculates power factor from VA/W ratings. Ideal for server rack planning, homelab power budgeting, network closet UPS selection, and graceful shutdown timer configuration."
method: POST
path: "/api/ups_runtime"
tags: ["power"]
---

# Estimates UPS (Uninterruptible Power Supply) backup runtime from battery specifications and connected load. Takes VA rating, watt rating, load in watts, and battery configuration (count, voltage, amp-hours) to compute effective stored energy after efficiency losses and runtime in minutes and hours. Detects overload conditions when load exceeds the UPS watt rating. Calculates power factor from VA/W ratings. Ideal for server rack planning, homelab power budgeting, network closet UPS selection, and graceful shutdown timer configuration.

`POST /api/ups_runtime`

## Request

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

## Request body

- object
  - `va_rating` number, required: UPS VA (volt-ampere) rating
  - `watt_rating` number, required: UPS real power (watt) rating
  - `load_watts` number, required: Connected load in watts
  - `battery_count` number: Number of batteries in the UPS
  - `battery_voltage` number: Voltage per battery (V)
  - `battery_ah` number: Capacity per battery in amp-hours (Ah)
  - `efficiency` number: Inverter/conversion efficiency (0-1), default 0.9

## Response `200`

Computed result for ups_runtime

- object
  - `result` object, required
    - `runtime_minutes` number, required: Estimated backup runtime in minutes
    - `runtime_hours` number, required: Estimated backup runtime in hours
    - `load_pct` number, required: Load as percentage of UPS watt capacity
    - `battery_wh` number, required: Total battery energy in watt-hours (before efficiency)
    - `effective_wh` number, required: Usable battery energy after efficiency losses (Wh)
    - `pf` number, required: Power factor (watt_rating / va_rating)
    - `overloaded` boolean, required: True if load exceeds UPS watt rating
  - `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)