Volts to Watts Calculator

Formula Used

Real power depends on system type. Apparent power helps compare loading and equipment ratings.

• DC: P(W) = V × I × η
• AC (Single‑Phase): P(W) = V × I × PF × η
• AC (Three‑Phase, line‑to‑line V): P(W) = √3 × V × I × PF × η
• Apparent power: S(VA) = V × I (single/DC), S(VA) = √3 × V × I (three‑phase)
• Energy: E(kWh) = (P/1000) × hours, Cost: E × rate
• Breaker suggestion: I_breaker ≈ 1.25 × I_load (typical continuous-load practice)

Always follow local electrical codes, equipment nameplates, and engineering judgment.

How to Use This Calculator

1. Select the electrical system: DC, single‑phase AC, or three‑phase AC.
2. Enter measured or rated voltage and current.
3. For AC, set a realistic power factor (motors often 0.7–0.95).
4. Optionally enter efficiency to derate for real-world losses.
5. Set runtime and energy rate if you need cost estimates.
6. Press Calculate to view results above the form.
7. Use the CSV or PDF buttons to export the computed report.

Example Data Table

Sample scenarios for common jobsite electrical systems.

Values are illustrative; use your own field measurements for planning and verification.

Practical Notes for Construction Work

• Use nameplate data for equipment sizing, then validate with measurements.
• Consider starting currents, voltage drop, and duty cycle for motors.
• For generators, compare both watts (real) and VA (apparent).
• Keep margins for temperature, cable routing, and future load growth.

Professional Field Guide

1) Why watts matter on site

Wattage is the usable power that actually performs work. In construction, it helps you match tools, heaters, welders, and temporary lighting to circuits, generators, and distribution boards without nuisance trips or overheated conductors.

2) Typical voltage ranges you will see

Common values include 120 V and 240 V for portable tools, 230 V in many regions for single‑phase equipment, and 400 V line‑to‑line for three‑phase plant. Always confirm whether a three‑phase value is line‑to‑line or line‑to‑neutral.

3) Current readings: nameplate vs clamp meter

Nameplates provide rated current at stated conditions, while clamp meters show real operating current. Use measurements during steady operation, then compare to the nameplate. If current rises, check voltage drop, binding loads, or incorrect connections.

4) Power factor data for real jobs

Resistive loads such as heaters and incandescent lamps are near PF 1.00. Inductive loads such as motors and compressors often fall between PF 0.70 and 0.95 depending on size and loading. Lower PF reduces real watts for the same volts and amps.

5) Efficiency and losses you should budget

Motors, inverters, and long cable runs introduce losses. Efficient equipment may run 90–95% under good conditions, while harsh duty cycles and heat reduce performance. Use the efficiency input to derate watts when planning generator capacity and heat rise.

6) Three‑phase power: the √3 factor

For balanced three‑phase systems, real power uses √3 × V(line‑to‑line) × I × PF × η. This calculator applies that automatically when you select three‑phase. It is useful for pumps, hoists, mixers, and larger temporary distribution systems.

7) Breaker sizing and continuous loads

A common field rule is to size overcurrent protection near 125% of expected continuous current, then verify with local code requirements and equipment instructions. Starting currents for motors can be several times running current, so use proper motor protection methods.

8) Energy, kWh, and cost planning

Converting watts to kWh supports rental, fuel, and utility planning. For example, a 2.3 kW heater running 6 hours consumes 13.8 kWh. Multiply by your tariff to estimate cost, and include generator efficiency and fuel curves for tighter budgets.

FAQs

1) Can I use this for DC battery tools?

Yes. Select DC, enter volts and amps, and optionally set efficiency to reflect converter or wiring losses. The result estimates real watts delivered by the source.

2) What power factor should I enter for a motor?

Many loaded induction motors operate around 0.80–0.95. If you do not know the value, start with 0.90 and compare calculated watts against nameplate kW when available.

3) Why do I see both VA and W?

VA is apparent power and reflects total current demand. W is real power that does work. Generators and transformers are often rated in VA or kVA, so both values help with sizing.

4) Does three‑phase voltage mean line‑to‑line?

In most field contexts, yes. This calculator assumes three‑phase voltage is line‑to‑line. If you have line‑to‑neutral, convert it to line‑to‑line before entering.

5) How accurate is the breaker suggestion?

It is a planning estimate using 125% of load current. Final sizing depends on local code, conductor selection, ambient temperature, and equipment instructions, especially for motors and welders.

6) How do I estimate cost for temporary power?

Enter runtime hours and your energy rate per kWh. The calculator multiplies kW by hours to get kWh, then multiplies by your rate for an estimated cost.

7) Should I include efficiency for extension cords?

You can, especially for long runs or high current. Efficiency acts as a simple derate. For detailed work, calculate voltage drop and conductor heating separately, then compare with site requirements.