Tools in This Collection
Residential Electrical Load Calculator
Tally panel load against service size using NEC Article 220 methods
Voltage Drop Calculator
Check that branch circuit runs stay within the 3% voltage drop threshold
Wire Ampacity Calculator
Confirm conductor gauge handles the load for any circuit
Conduit Fill Calculator
Verify wire bundle fits inside conduit per NEC 40% fill limit
Electrical Box Fill Calculator
Ensure boxes are not overcrowded with conductors and devices
Water Supply Pipe Sizing Calculator
Determine proper pipe diameter for main lines and branch runs
Pipe Volume Calculator
Calculate water volume in any pipe run for expansion tank sizing
Gas Line Sizing Calculator
Size natural gas and propane pipe runs by BTU load and run length
Water Heater Size Calculator
Match water heater tank capacity to peak household demand
Water Velocity in Pipes Calculator
Verify flow velocity stays below limits that cause pipe erosion and noise
Size Electrical and Plumbing Systems Correctly
Electrical work requires precise sizing — undersized wire is a fire hazard, and oversized conduit wastes money on unnecessary upsizing. Most residential homes have 200-amp service, which handles about 40,000 watts of connected load at 80% capacity. These calculators use NEC code-based methods to verify your electrical and plumbing sizing before you pull permits or purchase materials.
Electrical Load and Wire Sizing
Start with the Residential Electrical Load Calculator to tally your panel load against service size. NEC Article 220 allows you to count only 100% of the first 10,000 VA of general lighting and small appliance loads, plus 40% of the remaining load. For a typical 2,000 sq ft home, the calculated load is usually 80-120 amps — well within 200-amp service limits.
For wire runs, the Voltage Drop Calculator checks that long branch circuit runs stay within the 3% threshold. A 20-amp, 120V circuit running 75 feet with 12 AWG wire drops 2.8% — borderline acceptable. Runs over 100 feet may require upsizing to 10 AWG to stay compliant. The Wire Ampacity Calculator confirms your conductor gauge handles the load: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps in typical residential installations.
Conduit and Box Fill
The Conduit Fill Calculator verifies that your wire bundle fits inside your conduit — NEC limits fill to 40% of conduit cross-section for 3 or more conductors. Three 12 AWG THHN wires fit in 1/2-inch EMT with room to spare; six wires require 3/4-inch conduit. The Electrical Box Fill Calculator ensures you're not overcrowding boxes with too many conductors, devices, and clamps — a common cause of inspection failures.
Plumbing: Pipe Sizing and Water Systems
Water supply pipe sizing depends on fixture units and flow demand. The Water Supply Pipe Sizing Calculator determines proper pipe diameter for main lines and branch runs. A 3/4-inch main supply handles up to 20 fixture units; a 1/2-inch branch handles up to 6. The Pipe Volume Calculator calculates water volume in any run — useful for sizing expansion tanks and pressure vessels.
For water heater replacement, the Water Heater Size Calculator matches tank capacity to peak household demand based on occupant count and usage patterns. A household of 4 typically needs a 50-gallon tank. The Gas Line Sizing Calculator determines pipe diameter for natural gas or propane runs based on BTU load and run length, and the Water Velocity in Pipes Calculator verifies flow velocity stays below the 8 ft/s limit that causes pipe erosion and noise.
Frequently Asked Questions
What size electrical service does a typical home need?
Most homes built after 1980 have 200-amp service, which is adequate for standard loads including central air conditioning, electric range, electric dryer, and general lighting. Homes with electric vehicle chargers, hot tubs, or multiple large appliances may require a 400-amp service upgrade. The Electrical Load Calculator tallies your specific loads to determine if your current service size is sufficient.
What wire gauge do I need for a 20-amp circuit?
A 20-amp, 120V branch circuit requires 12 AWG copper wire (or 10 AWG aluminum, though aluminum is not recommended for branch circuits). 14 AWG wire is only rated for 15-amp circuits. Using 14 AWG on a 20-amp circuit is a code violation and fire hazard. Always match wire gauge to the breaker amperage.
How do I size a gas pipe for my appliances?
Gas pipe sizing depends on the total BTU load of all connected appliances and the length of the run from the meter. A 1/2-inch pipe can handle about 100,000 BTU at 10 feet; the same pipe only handles 50,000 BTU at 100 feet due to pressure drop. The Gas Line Sizing Calculator determines the minimum pipe diameter for your BTU load and run length for both natural gas and propane.
What size water heater do I need for my household?
General guidelines: 1-2 people = 30-40 gallon tank, 2-4 people = 40-50 gallons, 4-6 people = 50-80 gallons. Tankless water heaters are sized by flow rate (GPM) rather than storage volume. The Water Heater Size Calculator takes into account peak demand based on the number of simultaneous fixtures that might run at once.