EVERY ENERGY EFFICIENCY DECISION · WITH THE MATH SHOWN

Energy Efficiency Calculators

Optimize your home energy use — BTU sizing, wire gauges, EV charging, heat pumps, and full energy audits. Free calculators to cut costs and carbon.

Start with BTU Calculator →
  • BTU Calculator

    Popular

    Heating and cooling BTU needs based on room size, insulation, and climate zone.

    →
  • Wire Size Calculator

    Correct wire gauge for amperage, distance, and voltage drop requirements.

    →
  • Pipe Size Calculator

    Pipe diameter for target flow rate and pressure based on fixture count.

    →
  • Water Heater Size Calculator

    Tank or tankless water heater capacity for your household demand.

    →
  • EV Charging Cost Calculator

    Monthly and per-mile charging cost for your electric vehicle at home or public stations.

    →
  • Heat Pump Calculator

    Heat pump sizing, energy savings, and payback period versus furnace or AC.

    →
  • Home Energy Audit Calculator

    Identify energy waste and estimate annual savings from insulation, sealing, and upgrades.

    →
  • kWh Calculator

    Calculate kilowatt-hour usage and monthly cost for any appliance or circuit.

    →
  • Solar Panel Calculator

    System size, output, and savings for residential solar by roof area and sunlight.

    →
Related money decisions
  • Home Improvement Calculators
    →
  • Cost Guides
    →
  • All Calculators
    →

Written and maintained by Jere Salmisto, Founder, CalcFi. Updated May 17, 2026.

Formulas cited to primary US government and regulatory sources. Methodology at /about/editorial. Published by CalcFi Editorial.