Free calculators

Quick, accurate calculators for your paycheck and your trade. No sign-up, nothing to install. Every one has a worked example, the formula behind it, and an app that does the same thing offline.

Pay & taxes

Take-home pay for every state, self-employment tax, hourly-to-salary and the mileage deduction.

Take-Home Pay Calculator: All 50 States + DC (2026)

Your paycheck after federal, state and payroll taxes. Every state and DC, 2026 tax rules.

Self-Employment Tax Calculator (2026)

SE tax, income tax and quarterly payments for contractors and 1099 workers.

Hourly to Salary Calculator (with Overtime)

Convert hourly pay to a yearly salary or back, with overtime.

Mileage Deduction Calculator (2026 IRS Rates)

Business, medical and charity miles at the 2026 IRS rates, with estimated tax savings.

Electrical

Voltage drop, wire size, conduit fill, Ohm's law, three-phase power and conduit bending.

Voltage Drop Calculator

Percent voltage drop for any wire size and run length, plus the smallest wire that passes.

Wire Size Calculator (NEC Ampacity)

Wire size and breaker from load amps, with continuous-load and derating.

Conduit Fill Calculator (EMT, RMC, PVC)

Fill percent and the minimum conduit size for THHN wires.

Ohm's Law Calculator

Enter any two of volts, amps, ohms or watts and get the other two.

Three-Phase Power Calculator (kW, kVA, Amps)

Amps, kVA and kW for single- and three-phase loads.

Conduit Bending Calculator (Offset, Saddle, Stub-Up)

Offset spacing, shrink, 3-bend saddles and stub-up marks.

HVAC / refrigeration

Superheat and subcooling, refrigerant pressure-temperature charts, airflow, ductwork and AC sizing.

Superheat and Subcooling Calculator

Superheat and subcooling from your gauge pressures and line temperatures, with target superheat.

Refrigerant Pressure-Temperature (P/T) Chart

Saturation temperature and pressure for 8 refrigerants, with a full chart.

CFM to BTU Calculator (Airflow and Heating Load)

Solve for CFM, BTU/hr or delta T with the sensible heat equation.

Duct Size Calculator (Round and Rectangular)

Round and rectangular duct sizes from CFM and friction rate, with velocity.

AC Sizing Calculator: BTU and Tons for Your Home

A quick BTU and tonnage estimate for a house or room.

Plumbing & piping

Pipe friction loss and velocity, and offset calculations for pipefitters.

Pipe Friction Loss Calculator (Hazen-Williams)

Pressure drop and velocity for copper, steel and PVC pipe.

Pipe Offset Calculator

Offset travel, run and cut length for any fitting angle.

Fire protection

Fire alarm battery and NAC voltage drop, plus sprinkler K-factor and friction-loss calculators.

Fire Alarm Battery Calculator (NFPA 72)

Required amp-hours for 24 or 60 hours of standby plus alarm, with the 20% margin.

NAC Voltage Drop Calculator (Fire Alarm Circuits)

End-of-line voltage and the minimum wire gauge for a notification circuit.

Sprinkler K-Factor Calculator (Flow and Pressure)

Flow from pressure, pressure from flow, or K-factor from a flow test.

Sprinkler Pipe Friction Loss Calculator (NFPA 13)

Friction loss, velocity and end pressure for sprinkler piping.

Construction

Concrete volume, stair stringers, and roof pitch and rafter length.

Concrete Calculator: Cubic Yards and Bags

Cubic yards and bag counts for slabs, footings and round columns.

Stair Stringer Calculator

Riser count, tread run and stringer length from your total rise.

Roof Pitch and Rafter Length Calculator

Rafter length, angle, roof area and squares from pitch and span.

Trucking

Cost per mile and trip profit for owner-operators.

Trucking Cost Per Mile Calculator (Owner-Operators)

Your true cost per mile, break-even rate and monthly profit.

Take-home pay by state

Pick your state for a paycheck calculator with its own tax rules, rates and payroll deductions.

Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware District of Columbia Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming

These calculators give estimates for planning and are not tax, legal or engineering advice. Confirm code-related results against the adopted code edition and your authority having jurisdiction, and tax results against your pay stub or a tax professional.