Convert between Power and Current with Ease
This calculator helps you convert between watts (power) and amps (current) for both DC and AC electrical systems.
Enter your values and select the appropriate circuit type to get accurate calculations.
Enter Your Values
Calculation Results
Enter your values and click “Calculate” to see the results.
Formula Used
For direct current (DC) circuits, the calculation is straightforward using Ohm’s Law.
Common Examples
- 100W bulb at 120V = 0.83A
- 1500W heater at 120V = 12.5A
- 500W PC at 240V = 2.08A
- 2000W appliance at 110V = 18.18A
Watts (Power)
Watts measure the rate of energy conversion or transfer. In electrical terms, it’s the product of voltage and current.
Amps (Current)
Amps measure the flow of electrical charge. It represents how many electrons are passing a point per second.
Volts (Voltage)
Volts measure electrical potential difference – the “pressure” that pushes electrons through a circuit.
Power Factor
In AC circuits, power factor represents the efficiency of power usage. It ranges from 0 to 1, with 1 being most efficient.
A watts to amps calculator helps you determine the current drawn by a device from its power rating and supply voltage. This is essential for choosing wire sizes, circuit breakers, generators, and inverters. Below you�ll find the exact formulas for DC, AC single-phase, and AC three-phase systems, how to include power factor (PF), and clear examples you can follow or replicate in your own spreadsheet.
Core Formulas
1) DC Circuits
I=PVI = \frac{P}{V}I=VP?
- III = current (amps, A)
- PPP = power (watts, W)
- VVV = voltage (volts, V)
2) AC Single-Phase (with Power Factor)
I=PV�PFI = \frac{P}{V \times \text{PF}}I=V�PFP?
- PF ranges 0�1 (typical 0.8�0.95 for many appliances).
- If PF is unknown, 0.8 is a conservative planning value.
3) AC Three-Phase (with Power Factor)
I=P3�Vline�PFI = \frac{P}{\sqrt{3} \times V_\text{line} \times \text{PF}}I=3?�Vline?�PFP?
- VlineV_\text{line}Vline? is the line-to-line voltage (e.g., 400 V in many regions, 480 V in some industrial setups).
Note: For apparent power SSS in volt-amperes (VA):
Single-phase: S=V�IS = V \times IS=V�I ? I=SVI = \frac{S}{V}I=VS?
Three-phase: S=3?VlineIS = \sqrt{3}\, V_\text{line} IS=3?Vline?I ? I=S3?VlineI = \frac{S}{\sqrt{3}\, V_\text{line}}I=3?Vline?S?
Quick Reference Table (Typical PF Assumptions)
| Scenario | Given | Formula | Result (I) |
|---|---|---|---|
| DC example | 240 W @ 24 V | I=P/VI=P/VI=P/V | 10 A |
| AC 1-phase | 1500 W @ 120 V, PF 0.9 | I=P/(V?PF)I=P/(V�PF)I=P/(V?PF) | 13.9 A |
| AC 1-phase | 2000 W @ 230 V, PF 0.85 | I=P/(V?PF)I=P/(V�PF)I=P/(V?PF) | 10.3 A |
| AC 3-phase | 10 kW @ 400 V, PF 0.85 | I=P/(3?V?PF)I=P/(\sqrt{3}�V�PF)I=P/(3??V?PF) | 17.0 A |
| AC 3-phase | 20 kW @ 480 V, PF 0.9 | I=P/(3?V?PF)I=P/(\sqrt{3}�V�PF)I=P/(3??V?PF) | 26.7 A |
(Results rounded.)
Worked Examples
Example 1 � DC Solar Load
A 300 W DC pump on a 24 V battery bank: I=30024=12.5 AI=\frac{300}{24}=12.5\text{ A}I=24300?=12.5 A
Select wiring and fusing safely above 12.5 A (see safety tips below).
Example 2 � Single-Phase Appliance
A 1800 W space heater on 120 V, PF ? 1 (purely resistive): I=1800120�1.0=15 AI=\frac{1800}{120\times 1.0}=15\text{ A}I=120�1.01800?=15 A
On North American circuits, 15 A is the typical breaker rating; continuous loads should be derated (see 80% rule).
Example 3 � Three-Phase Motor
A 7.5 kW motor at 400 V, PF = 0.82: I=75003�400�0.82=75001.732�400�0.82?13.2 AI=\frac{7500}{\sqrt{3}\times 400\times 0.82} =\frac{7500}{1.732\times 400\times 0.82} \approx 13.2\text{ A}I=3?�400�0.827500?=1.732�400�0.827500??13.2 A
Planning & Sizing Tips
- Continuous Load Rule (NEC guideline):
For loads operating 3 hours or more, size the circuit at 125% of calculated current (i.e., use only 80% of a breaker�s rating).
Example: 15 A continuous ? plan for at least 18.75 A capacity ? typically a 20 A circuit. - Voltage Drop:
Long cable runs increase voltage drop and current heating. Consider larger wire gauges to keep voltage drop under ~3�5% for efficiency and device protection. - Power Factor Matters:
Motors, compressors, and switching power supplies often have PF < 1. Using PF = 1 can underestimate current�include PF if known. - Start-Up (Inrush) Current:
Motors and compressors can draw 2�7� running current on start. Check nameplate data and manufacturer specs. - Safety First:
When unsure, consult a licensed electrician, especially for mains wiring, breaker sizing, and code compliance.
DIY Spreadsheet Setup (No External Tool Needed)
Columns: Power (W), Voltage (V), PF, Phases
- DC:
= [Power] / [Voltage] - AC 1-phase:
= [Power] / ([Voltage] * [PF]) - AC 3-phase:
= [Power] / (SQRT(3) * [Voltage] * [PF])
Add conditional logic to switch formulas based on �Phases�.
FAQs
1) What if my device lists VA instead of W?
Use VA directly to find current: Single-phase I=S/VI=S/VI=S/V; three-phase I=S/(3V)I=S/(\sqrt{3}V)I=S/(3?V). VA already includes power factor implicitly as apparent power.
2) I don�t know the power factor. What should I use?
For planning, 0.8�0.9 is common for many AC loads. For heaters or incandescent lamps, PF ? 1.
3) Does frequency (50/60 Hz) change the formula?
No, but PF and nameplate current can differ slightly between 50 Hz and 60 Hz models.
4) Can I just divide watts by volts for AC?
Only if PF ? 1. Otherwise you�ll underestimate current.
5) How do I size the breaker?
Calculate current with the proper formula, apply the 125% continuous load rule if applicable, then select the nearest standard breaker and wire gauge per local code.
Conclusion
A watts to amps calculator is indispensable for electrical planning. Use the correct formula for DC, AC single-phase, or AC three-phase, and always account for power factor with AC loads. With accurate current estimates, you�ll choose the right wires, breakers, and power equipment�and avoid overheating, tripping, and costly rework.
