Enter Electrical Details
All calculations use real power and the selected operating duration.
Example Data Table
These examples assume one device and one operating cycle.
| Supply | Current | Voltage | Power Factor | Runtime | Power | Energy |
|---|---|---|---|---|---|---|
| DC | 10 A | 12 V | 1.00 | 4 h | 120 W | 480 Wh |
| AC single phase | 2 A | 230 V | 0.90 | 3 h | 414 W | 1,242 Wh |
| AC three phase | 5 A | 400 V | 0.85 | 2 h | 2,944 W | 5,889 Wh |
Formula Used
DC power: W = V × A
Single-phase AC power: W = V × A × PF
Three-phase AC power: W = √3 × V × A × PF
Input energy: Wh = W × hours × device quantity
Useful output energy: Useful Wh = input Wh × efficiency ÷ 100
Cost uses input energy: cost = kWh × electricity rate. The 30-day estimate multiplies your daily energy by 30.
How to Use This Calculator
- Enter the current in amperes from a meter or equipment label.
- Enter the matching operating voltage and choose the circuit type.
- For AC loads, add the rated power factor. Use 1.00 when it is unknown only for a rough estimate.
- Enter runtime and select minutes, hours, or days.
- Add the number of devices and typical daily operating cycles.
- Enter efficiency to estimate useful output energy, then add your electricity tariff to estimate cost.
- Press Calculate Watt Hours. Review the result above the form or export it as CSV or PDF.
Understanding Amps and Watt-Hours
Amps measure electrical current. They show how much charge moves through a circuit each second. Watt-hours measure energy. They show how much electricity a device uses or produces over time. Current alone cannot show energy use. You also need voltage and operating time. This calculator joins those values into useful energy results. It supports direct current, single-phase alternating current, and three-phase alternating current. That makes it useful for household devices, workshop tools, battery systems, and industrial equipment. The result can help you compare loads, estimate electricity costs, or size storage systems.
Why Voltage and Runtime Matter
Voltage pushes electrical current through a circuit. Higher voltage creates more power when current stays constant. Runtime then converts power into energy. A ten-amp device at twelve volts uses less power than a ten-amp device at two hundred thirty volts. The amp reading is identical, but the energy result is very different. Always use the voltage that matches the appliance or system. Enter the actual operating duration. Minutes are converted into hours automatically. Days are also converted before calculation. Add the number of identical devices when several units run together. This produces a combined energy estimate for the selected period.
Power Factor and Electrical Type
Direct-current calculations use volts multiplied by amps. Alternating-current loads may also need power factor. Power factor reflects the share of supplied electrical power that becomes real working power. Resistive loads, such as heaters, often have a power factor close to one. Motors, transformers, and some electronic devices can have lower values. Use the label value when it is available. For single-phase circuits, real power equals voltage multiplied by current and power factor. Three-phase systems also use the square root of three. Selecting the correct circuit type prevents major errors. Line-to-line voltage is normally used for the three-phase option.
Efficiency and Cost Planning
Efficiency is shown separately because it describes useful output energy. Electrical input energy is still used for consumption and cost estimates. A battery charger may draw one energy amount from the outlet while delivering a smaller amount to its battery. Enter the expected efficiency to see that delivered value. Leave it at one hundred percent when efficiency is unknown or irrelevant. Add an electricity rate to estimate operating cost. The estimate is only as reliable as your inputs. Equipment may draw more current during startup. Voltage can vary. Power factor can change with load. Use measured values for careful planning. Keep a safety margin when selecting wiring, inverters, generators, or batteries.
Limits and Safe Use
This tool is an estimate, not a replacement for electrical testing. Check circuit ratings before connecting equipment. Never select cables or breakers from energy totals alone. Current capacity, conductor length, ambient temperature, installation method, and local rules also matter. Ask a qualified electrician when work involves fixed wiring, high voltage, large batteries, or three-phase equipment in commercial settings. Review nameplate data and confirm measurements with suitable meters before making purchasing, safety, or installation decisions for complicated systems or uncertain loads.
Frequently Asked Questions
1. Can amps be converted directly to watt-hours?
No. Amps describe current. Watt-hours describe energy over time. You need voltage and runtime, plus power factor for many AC loads, to calculate watt-hours accurately.
2. What is the difference between watts and watt-hours?
Watts measure power at one moment. Watt-hours measure total energy used over a period. A 100-watt device running for five hours uses 500 watt-hours.
3. Should I use line voltage for three-phase power?
Yes. This calculator uses line-to-line voltage for the three-phase formula. Confirm your equipment label or electrical drawings before entering the voltage.
4. Why does the calculator ask for power factor?
Power factor converts apparent AC power into real working power. It matters for motors, transformers, and some electronic loads. It does not change the basic DC calculation.
5. What efficiency should I enter?
Enter the expected energy conversion efficiency for useful output. Use 100 percent when you only need electrical input energy or do not have an efficiency value.
6. Does the cost result include utility taxes?
No. The estimate multiplies calculated kWh by the rate you enter. Add taxes, fixed fees, tiered pricing, and demand charges separately when they apply.
7. Can I calculate battery energy with this tool?
Yes. Select DC, enter battery voltage, current, and runtime. Use efficiency to estimate energy delivered after charger, inverter, or battery losses.
8. Why might measured energy differ from the estimate?
Voltage, current, power factor, temperature, and loading conditions can change during operation. Startup surges and cycling also affect real energy use.
9. Can I use minutes instead of hours?
Yes. Select minutes as the runtime unit. The calculator divides minutes by 60 before finding watt-hours.
10. Is the monthly estimate always exact?
No. It assumes the entered daily use repeats for 30 days. Actual schedules, seasonal changes, and appliance behavior can change monthly consumption.
11. Is this calculator suitable for wire or breaker sizing?
No. Energy totals do not determine safe conductor or breaker sizes. Use better inputs for safer electrical planning results today.