Measure twice. Calculate once.
Free home improvement calculators for roofing, HVAC and electrical
Free calculators for US homeowners, built from public data and tested formulas. Every result shows the math, so you can check it before you buy materials or sign a quote.
Roofing
Measure once, then let the numbers carry through. Each tool hands its result to the next step, from pitch to roof area to materials.
- Attic Ventilation Calculator
Net free vent area under the IRC 1/150 and 1/300 rules, with ridge, box and soffit vent counts.
- Gutter Size Calculator
Gutter size and downspout count from roof area, pitch and NOAA rainfall intensity for your state.
- Metal Roof Cost
Metal roof price by type and state, compared with shingles up front and per year of life.
- Roof Pitch Calculator
Pitch, angle, slope and multiplier from rise and run, degrees or x/12. Includes rafter length.
- Roof Replacement Cost
Low, typical and high cost for a new shingle roof, using roofer wages from your state.
- Roof Square Footage Calculator
Sloped roof area and roofing squares from house size and pitch, with waste and edge lengths.
- Shingle Calculator
Shingle bundles from roof area, with waste, starter strip, hip and ridge cap and nails.
- Underlayment Calculator
Rolls of synthetic or felt underlayment and ice barrier, with the code's low-slope and eave rules.
HVAC
Start with the load, the heat your house gains in summer and loses in winter, then pick equipment, compare efficiency and estimate the cost.
- AC Size Calculator
Cooling load and central AC size in tons from your state's climate, windows and insulation.
- Duct Size Calculator
Round and rectangular duct sizes from CFM or tons, with friction rate and velocity checks.
- Furnace Size Calculator
Heat loss and gas furnace input size in BTU from your state's NOAA winter design temperature and AFUE.
- Heat Pump Size Calculator
Heat pump tons, balance point and backup heat in kW from your state's NOAA design temperatures.
- HVAC Replacement Cost
Installed price for an AC, heat pump, furnace or mini-split, using HVAC wages from your state.
- SEER Savings Calculator
Annual cooling cost and savings for a higher SEER2 unit, from your state's electricity price and climate.
Electrical
Plan the numbers before you call an electrician, from what a device costs to run to how big a generator or wire run needs to be.
- Electricity Cost Calculator
Cost to run any device per hour, day, month and year from its watts and your state's price.
- EV Charging Cost Calculator
Home EV charging cost per mile and per year in your state, compared with a gas car.
- Generator Size Calculator
Running and starting watts for your outage loads and the generator size that covers them.
- Voltage Drop Calculator
Voltage drop for copper or aluminum wire and the smallest AWG size within your target percent.
Why trust these numbers
- Formulas you can see
Each page shows the formula, the assumptions and a worked example.
- Public data, dated
Wages from BLS, energy prices from EIA, climate and hail from NOAA, each with its year.
- Tested code
Every calculation has automated tests and a hand-checked example before it goes live.