For data center engineers & facility managers · Vendor-neutral

Critical-facility planning, with the math in view.

Transparent planning calculators for critical facilities.

A mobile-friendly toolkit for eight critical-facility calculations, with the inputs and method behind each estimate in view.

Explore the calculatorsSee the method

Free. No account, no license server, no sales call.

UPS runtime / Cooling load / Rack power / PUE / Generator sizing / Cooling airflow / Dew point / kW / kVA / amps

Works offline · Install as an app
Live calculation preview
Read-only sample

UPS runtime, with the math in view.

3 h 27 minplanning estimate

Default inputs: 1,000 W load · 4 × 12 V, 100 Ah batteries · 90% efficiency · 80% remaining capacity.

Usable energy (Wh) = battery-bank energy × (UPS efficiency % ÷ 100) × (remaining battery capacity % ÷ 100)

Current calculation

  1. 12 V × 100 Ah × 4 batteries × 1 strings = 4,800 Wh
  2. 4,800 Wh × (90% ÷ 100) × (80% ÷ 100) = 3,456 Wh
  3. 3,456 Wh ÷ 1,000 W = 3.46 h; rounded to the nearest minute = 3 h 27 min
Nominal bank energy
4,800 Wh
Usable energy after factors
3,456 Wh
Runtime in seconds
12,441.6 seconds

Assumptions and limits

  • The bank starts fully charged.
  • The load is constant real power measured in watts.
  • Series and parallel capacity arithmetic is ideal.
  • Nameplate Ah is treated as available energy before the explicit efficiency and remaining-capacity factors.
  • No chemistry-specific Peukert or discharge-rate curve is applied.
  • No temperature correction is applied.
  • No inverter cutoff, battery-management limit, power-factor or inrush behavior, or manufacturer calibration is modeled.

Every result is an estimate for planning only—not a substitute for a licensed engineer’s design or manufacturer data.

Open the UPS runtime calculator →

The toolkit / 08 calculators

Eight planning calculators. One clear method.

Built for engineers, facility managers, technicians, MEP consultants, and students who want to inspect the reasoning—not just copy a number.

Not for: stamped construction documents, final equipment selection, or model-specific runtime guarantees. Use a licensed engineer and manufacturer data for those.

Browse all calculators
  1. 01

    UPS runtime

    Estimate runtime from load, battery-bank configuration, UPS efficiency, and remaining capacity.

    Read the UPS runtime calculator guide

    LOAD · BANK CONFIGURATION · EFFICIENCY · REMAINING CAPACITY

  2. 02

    Cooling load

    Build a cooling-load estimate from IT demand, lighting, people, and the building envelope.

    Read the data center cooling load calculator guide

    IT LOAD · LIGHTING · PEOPLE · ENVELOPE

  3. 03

    Rack power

    Plan rack power density and evaluate PDU capacity around the intended load.

    RACK DENSITY · POWER · PDU CAPACITY

  4. 04

    PUE

    Estimate power usage effectiveness, data center infrastructure efficiency, and non-IT overhead from facility and IT power.

    FACILITY POWER · IT POWER · PUE · DCiE

  5. 05

    Generator sizing

    Estimate standby generator kW and kVA requirements with running-load, power-factor, margin, and motor-start inputs.

    RUNNING LOAD · POWER FACTOR · MARGIN · MOTOR START

  6. 06

    Cooling airflow

    Estimate sensible airflow in CFM from heat load and temperature rise.

    SENSIBLE LOAD · TEMPERATURE RISE · AIRFLOW

  7. 07

    Dew point & humidity

    Find dew point, relative humidity and grains of moisture, and check condensation margin against the ASHRAE recommended envelope.

    TEMPERATURE · RELATIVE HUMIDITY · DEW POINT

  8. 08

    kW / kVA / amps

    Convert between kW, kVA and amps for single- and three-phase circuits, with power factor shown.

    kW · kVA · AMPS · POWER FACTOR

Comparing tools? LoadCairn vs vendor UPS calculators · vs spreadsheets · vs generator sizing software

Install once, work anywhere

Take LoadCairn into the data hall

Install LoadCairn on your phone or laptop. All eight calculators work offline, so you can size a UPS or check dew point in an electrical room or basement with no signal.

  • Works offline: UPS runtime, cooling load, airflow, rack power, generator sizing, kW/kVA/amps, PUE and dew point
  • Opens full-screen from your home screen, like a native app
  • Free, no app store, no account needed

A result you can review

No black-box numbers.

Each calculation keeps its working in frame, so a planning estimate can be understood in context and checked against the source information that matters to your facility.

Every result is traceable to its formula and its published source (ASHRAE, NIST or manufacturer data), so you can defend the number in a design review.

  1. 01 / TRACE

    Inputs

    The values and conditions behind the estimate stay visible.

  2. 02 / TRACE

    Formula + source

    See how the calculation is formed and where its method comes from.

  3. 03 / TRACE

    Assumptions

    Review the limits and assumptions before using the result for planning.

Planning estimate

Every result is an estimate for planning only—not a substitute for a licensed engineer’s design or manufacturer data.

Calculator FAQs

Individual or team

Calculate freely. Keep the work when you need to.

Every calculator is free for individual, unsaved use. Paid plans add the tools to retain work, share it, and bring it into project records.

Included with paid plans

  • Saved projects
  • Branded PDF reports
  • CSV exports
  • Shared team workspaces

Your saved estimates stay yours: export them as CSV at any time. Read the privacy policy.

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