ワットから アンペア 計算機
電流を求めるために、電力（ワット）とシステム電圧を入力してください。照明システム、小型家電、低電力の電子機器に最適です。
回路パラメータ
ワット → アンペア
安全な電流レベルは配線の過熱を防ぐのに役立ちます。
変換式
ワットからアンペアへの変換には回路電圧を知る必要があります。交流システムの場合は力率も必要です。
直流システム
I = W ÷ V オームの法則の最も単純な形です。直流回路ではワットをボルトで割るとアンペアが求まります。
単相AC
I = W ÷ (V × PF) 力率が1.0未満の交流負荷は、無効成分のためにワット定格が示す以上の電流を消費します。
三相AC
I = W ÷ (√3 × V × PF) 三相システムは電力を3つの相に分配します。線間電圧の変換には√3という係数が必須です。
How to Convert Watts to Amps
The watts-to-amps conversion is one of the most frequently used calculations in electrical work — from selecting the right fuse for an electronics project to sizing a circuit breaker for a household appliance. Watts measure real power consumed; amps measure the current flowing through the conductor. You need voltage (and power factor for AC) to bridge the two.
Watts vs. VA: What's the Difference?
Watts (W) measure real power — the energy actually converted to heat, light, or motion. Volt-Amperes (VA) measure apparent power — what the source must supply, including reactive current. For resistive loads (heaters, incandescent bulbs) they're equal. For inductive loads (motors, transformers), VA is always higher than watts.
Common Household Examples
- 1500W Space Heater at 120V DC: 1500 ÷ 120 = 12.5A. Needs a 15A circuit at minimum.
- 800W Microwave at 120V AC (PF 0.95): 800 ÷ (120 × 0.95) ≈ 7.0A. Comfortably fits a 15A circuit.
- 3000W Dryer at 240V AC (PF 1.0): 3000 ÷ 240 = 12.5A — typically wired on a 30A circuit to allow for startup transients.
Step-by-Step Conversion
- Find the Wattage: Check the device label, user manual, or measured consumption with a watt meter.
- Confirm the Voltage: Use the outlet voltage — 120V or 240V in North America; 230V in Europe.
- Apply the Power Factor: Use 1.0 for pure resistive loads (heaters, light bulbs). Use 0.8–0.9 for motors and most AC equipment.
- Size Your Protection: The calculated amps is the continuous draw. Size breakers and fuses at 125% of continuous load per NEC requirements.