Watts to Volts (W to V) + Volts to Watts (V to W), Formulas, Examples & Reference Table
Quick math: V = W ÷ A and W = V × A. Use the reference table for fast lookups (5A / 10A / 20A), and see the 3-phase + power factor section for AC accuracy.
Tip: For AC systems (especially motors), power factor and phase type can change real-world results.
DC vs 1-Phase vs 3-Phase (What Changes?)
Some converters and calculators include modes like DC AC-Single Phase AC-Three Phase. Here’s what changes (and why results can differ).
Mode 1: DC (Direct Current)
DC is the simplest case. If you know watts and amps, voltage is:
Mode 2: Single-Phase AC (Typical Homes)
Many quick conversions still use V = W ÷ A as an estimate. For better accuracy with AC loads (especially motors), include power factor (PF):
If PF is unknown, a common assumption is ~0.8–1.0 depending on the load.
Mode 3: Three-Phase AC (Industrial / High Power)
Three-phase uses three AC waveforms and is common for large motors and industrial equipment. A common balanced 3-phase formula is:
√3 ≈ 1.732 — that factor is why three-phase results often differ from DC or single-phase.
Formulas (Watts ↔ Volts)
Watts to Volts
Volts to Watts
Where W = watts, V = volts, A = amps.
How to Convert (Step-by-Step)
Convert Watts to Volts
- Find watts (W): from the device label or spec sheet.
- Find amps (A): from the label/spec sheet or measure current.
- Divide: V = W ÷ A.
Example: 500W at 5A → V = 500 ÷ 5 = 100V.
Convert Volts to Watts
- Find volts (V): supply voltage (e.g., 120V or 240V).
- Find amps (A): from the label/spec sheet or measure current.
- Multiply: W = V × A.
Example: 120V at 10A → W = 120 × 10 = 1200W.
Watts to Volts Reference Table (5A / 10A / 20A)
Quick lookup using sample currents of 5A, 10A, and 20A.
| Watts (W) | Volts (V) at 5A | Volts (V) at 10A | Volts (V) at 20A |
|---|---|---|---|
| 0.5 | 0.1 | 0.05 | 0.025 |
| 1 | 0.2 | 0.1 | 0.05 |
| 1.5 | 0.3 | 0.15 | 0.075 |
| 1.8 | 0.36 | 0.18 | 0.09 |
| 5 | 1 | 0.5 | 0.25 |
| 10 | 2 | 1 | 0.5 |
| 20 | 4 | 2 | 1 |
| 24 | 4.8 | 2.4 | 1.2 |
| 30 | 6 | 3 | 1.5 |
| 45 | 9 | 4.5 | 2.25 |
| 60 | 12 | 6 | 3 |
| 65 | 13 | 6.5 | 3.25 |
| 100 | 20 | 10 | 5 |
| 250 | 50 | 25 | 12.5 |
| 300 | 60 | 30 | 15 |
| 350 | 70 | 35 | 17.5 |
| 400 | 80 | 40 | 20 |
| 500 | 100 | 50 | 25 |
| 1000 | 200 | 100 | 50 |
| 1200 | 240 | 120 | 60 |
| 1500 | 300 | 150 | 75 |
| 1800 | 360 | 180 | 90 |
| 2000 | 400 | 200 | 100 |
| 10000 | 2000 | 1000 | 500 |
Note: This table is simple math. For AC motors and inductive loads, power factor can change real-world results.
Examples
Watts to Volts Examples (V = W ÷ A)
1000W
- At 5A: 1000 ÷ 5 = 200V
- At 10A: 1000 ÷ 10 = 100V
- At 20A: 1000 ÷ 20 = 50V
Volts to Watts Examples (W = V × A)
- 120V at 10A → 120 × 10 = 1200W
- 240V at 12.5A → 240 × 12.5 = 3000W
- 24V at 5A → 24 × 5 = 120W
What Is 3-Phase Power and Power Factor?
What Is Three-Phase Power?
Three-phase power delivers electricity using three AC waveforms instead of one. They’re offset, which makes power delivery smoother and more efficient.
Most homes use single-phase. Three-phase is common for factories, large motors, HVAC systems, and industrial equipment.
Why Three-Phase Is Used
- Delivers more power with the same current
- Runs motors more smoothly
- Reduces losses
- Often allows smaller cables for the same power
Three-Phase Power Formula (Balanced)
Where √3 ≈ 1.732.
What Is Power Factor (PF)?
Power factor describes how efficiently AC power is used. It ranges from 0 to 1. PF = 1.0 is ideal; motors and inductive loads often have lower PF.
Typical Power Factor Values
| Device Type | Typical PF |
|---|---|
| Resistive loads (heaters) | ~1.0 |
| LED lighting (varies) | ~0.7 – 0.9 |
| Motors / compressors | ~0.7 – 0.85 |
| Industrial equipment | ~0.8 – 0.95 |
How PF Changes the Calculation (Single-Phase AC)
Lower PF usually means higher current for the same real power, which can affect wiring size and heating.
FAQ
Can you convert watts to volts without amps?
No. Watts to volts requires current (amps). Use V = W ÷ A.
Can you convert volts to watts without amps?
No. Volts to watts also requires current. Use W = V × A.
Is the simple watts-to-volts formula accurate for AC?
It’s a good estimate. For motors and other inductive AC loads, include power factor (PF) for better accuracy.
What’s the difference between single-phase and three-phase?
Single-phase is common in homes. Three-phase uses three AC waveforms and is common in industrial/high-power systems because it delivers power more efficiently and runs motors smoothly.
What is power factor in simple terms?
Power factor shows how efficiently AC power is used. PF closer to 1.0 is better. Lower PF often means higher current for the same usable power.
