UPS Sizing Calculator

Calculate UPS capacity, battery requirements, and costs for your critical power protection needs

UPS Sizing Calculator

Calculate UPS capacity and battery requirements for your critical power needs

Watts

Total power consumption of all equipment to be protected

Typical values: Servers/IT 0.8-0.9, Motors 0.7-0.8, Mixed 0.8

minutes

How long the UPS should run on battery power

%

Additional capacity for future equipment (typically 20-30%)

%

Modern UPS efficiency: 93-96% typical

UPS Sizing Guide for UK Installations

Selecting the correct UPS (Uninterruptible Power Supply) capacity is critical for protecting your IT equipment, servers, and critical infrastructure from power outages, voltage fluctuations, and electrical disturbances.

Key Sizing Factors

  • Load Capacity (Watts/VA): UPS must handle your total equipment load plus a safety margin. Always size for peak load, not average.
  • Power Factor: Ratio of real power (Watts) to apparent power (VA). Modern IT equipment typically has PF of 0.8-0.9. UPS capacity is rated in VA, so divide your Watts by power factor.
  • Runtime Requirements: How long do you need to run on battery? Common targets: 10-15 minutes for orderly shutdown, 30-60 minutes for extended operation, or until generator starts.
  • Future Expansion: Plan for growth. Add 20-30% buffer for additional equipment over the next 3-5 years.
  • Redundancy: Critical applications may require N+1 (spare capacity) or 2N (full duplication) for high availability.

UPS Sizing Formula

Required VA = (Total Watts / Power Factor) × (1 + Expansion%) × Redundancy Factor

Battery Runtime = (Battery Ah × Voltage × Efficiency) / Load Watts

Installation Requirements

  • Electrical Supply: Small UPS (<10kVA) use single-phase 230V. Larger systems require three-phase 400V supply.
  • Circuit Protection: Dedicated circuit with appropriately rated MCB/MCCB. Upstream and downstream protection coordination essential.
  • Earthing: Proper earthing critical for safety and UPS operation. TN-S or TT systems preferred.
  • Environmental: Temperature 20-25°C optimal, humidity 40-60%, clean environment away from moisture and dust.
  • Ventilation: UPS systems generate heat (5-10% of rated power). Ensure adequate cooling and clearances.
  • Battery Room: Large systems may require separate battery room with ventilation (hydrogen gas), temperature control, and fire suppression.

Professional Installation Required

UPS systems over 3kVA should be installed by qualified electrical contractors familiar with critical power systems. Installation must comply with BS 7671 (18th Edition) and manufacturer specifications. Annual maintenance and battery testing essential for reliability.

UPS Types Explained

🔌

Offline / Standby UPS

Switchover Time: 5-10 milliseconds

Efficiency: 95-98% (very efficient)

Protection: Basic - power failure only

Best For: Workstations, small offices, non-critical equipment

Typical Sizes: 500VA - 2kVA

Cost: £80-£400

⚡

Line Interactive UPS

Switchover Time: 2-4 milliseconds

Efficiency: 93-96%

Protection: Voltage regulation + battery backup

Best For: Servers, network equipment, small to medium businesses

Typical Sizes: 1kVA - 5kVA

Cost: £300-£2,500

🏢

Online Double Conversion UPS

Switchover Time: Zero (continuous operation)

Efficiency: 90-95% (92-96% with eco mode)

Protection: Complete isolation and conditioning

Best For: Data centres, critical infrastructure, medical equipment, industrial

Typical Sizes: 5kVA - 800kVA+

Cost: £2,000-£500,000+

Common UPS Applications

Server Rooms & Data Centres

Typical requirements for server protection:

  • • Small rack: 3-6kVA, 15-20 min runtime
  • • Medium server room: 10-20kVA, 30 min runtime
  • • Data centre: 40kVA+ with N+1 redundancy
  • • Online double conversion UPS recommended
  • • Generator backup for extended outages

Industrial & Manufacturing

Protection for production systems:

  • • PLC and control systems: 1-3kVA
  • • Process equipment: 5-20kVA
  • • Manufacturing lines: 40kVA+
  • • Three-phase UPS for motor loads
  • • Short runtime to save production state

Medical & Healthcare

Critical healthcare power protection:

  • • Medical imaging: 10-30kVA
  • • Operating theatres: N+1 redundancy
  • • Critical care: 2N for maximum uptime
  • • Must meet HTM 06-01 standards
  • • Monthly testing and maintenance

Telecommunications

Network infrastructure protection:

  • • Network closets: 1-3kVA
  • • Telephone exchanges: 10-40kVA
  • • Cell towers: 5-10kVA with solar
  • • 24/7 operation requirements
  • • Remote monitoring essential

Cost of Downtime vs UPS Investment

Consider the cost of power interruptions when sizing your UPS:

  • • IT downtime: £3,000-£15,000 per hour (SME average)
  • • Manufacturing downtime: £10,000-£100,000 per hour
  • • Data loss and recovery: £5,000-£50,000 per incident
  • • Reputation damage: Difficult to quantify

A properly sized UPS system typically pays for itself after preventing just one major outage.