Electrical Calculators — Circuits, Power & Wiring

Multiply the appliance wattage by the hours of use to get watt-hours, then divide by 1,000 to get kilowatt-hours (kWh). Multiply by your electricity rate (found on your utility bill). For example, a 100W bulb running 10 hours uses 1 kWh. At $0.12/kWh, that costs $0.12 per day.

For a standard 20-amp, 120V branch circuit up to 50 feet, 12 AWG copper wire is the NEC minimum. For longer runs, you may need to upsize to 10 AWG to keep voltage drop below 3%. Our wire sizing calculator factors in current, distance, and voltage to recommend the correct gauge.

Voltage drop is the loss of voltage as current flows through wire resistance over distance. Excessive voltage drop (above 3% for branch circuits or 5% total) causes equipment to underperform, lights to dim, and motors to overheat. Proper wire sizing minimizes voltage drop and ensures safe, efficient operation.

Electricity cost is calculated as: Cost = (Power in kW × Hours used × Electricity rate per kWh)

Steps: 

1. Find the wattage of the device (from label or manual).
2. Convert to kilowatts (watts ÷ 1,000).
3. Multiply by hours of use per day/month.
4. Multiply by your utility rate (e.g., $0.12/kWh). Example: A 1,500 W heater running 4 hours/day at $0.15/kWh costs ≈ $0.90/day or $27/month. Our electricity cost calculator lets you input device wattage, usage hours, and local rate for instant monthly/annual estimates.

For a standard 20-amp circuit (most common for kitchen outlets, bathrooms, garages): 

• Use 12 AWG copper wire (rated for 20 amps at 120V or 240V under NEC rules).
• Never use 14 AWG (only good for 15 amps).
• For longer runs (>50–75 ft), consider upsizing to 10 AWG to reduce voltage drop.
• Aluminum wire: Use 10 AWG for 20 amps (but copper is preferred for safety). Always follow local electrical codes and consult a licensed electrician. Our wire size calculator helps you select the correct gauge based on amps, distance, voltage, and material.

Voltage drop is the reduction in voltage from the power source to the load due to resistance in the wires.

Why it matters: 

• Excessive drop (>3–5%) causes dim lights, inefficient motors, overheating, and equipment damage.
• It wastes energy and reduces appliance performance. Formula: Voltage drop = (2 × Length × Current × Resistance per foot) / 1000 (for single-phase). Keep drop under 3% for branch circuits, 5% total. Our voltage drop calculator computes exact drop percentage and recommends wire size upgrades if needed.

Power (P) = Voltage (V) × Current (I)
Or: P = V² / R (if resistance is known)
Or: P = I² × R

Examples: 

• 120 V outlet with 5 A device = 600 watts (0.6 kW).
• 240 V dryer drawing 10 A = 2,400 watts (2.4 kW). To find daily/monthly usage: multiply watts by hours, divide by 1,000 for kWh. Our power calculator instantly converts between watts, amps, volts, and kWh — perfect for sizing breakers, inverters, or estimating bills.