Quick Electrical Unit Converter
Pick a quantity, enter a value, choose the units — the result and the exact formula appear instantly.
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Common conversions
Ohm's Law Calculator
Fill in any two of voltage, current, resistance, or power — the other two are solved instantly, with the formulas used.
Enter any two values
Ohm's law & power triangles
Companion power triangle: P on top, V × I at the bottom — cover P to get P = V × I, cover V to get V = P ÷ I, cover I to get I = P ÷ V.
Power, Energy & Electricity Cost
P = V × I gives watts; energy = power × time gives kWh — what your bill charges for.
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- Power
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- Energy
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- Est. cost
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- Per day (24h)
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kW vs kWh: a kilowatt (kW) is the rate of energy use right now; a kilowatt-hour (kWh) is energy used over time. A 1.5 kW heater running 2 hours consumes 3 kWh.
Resistor Color Code Decoder
Pick the number of bands, then tap each band's color — the value, tolerance, and temperature coefficient appear instantly (IEC 60062).
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- Nominal
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- Tolerance
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- Range
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- Temp coeff.
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Reading guide
Orient the resistor so the gold or silver band is on the right — that is the tolerance band, read from the opposite end. 4-band: digit-digit-multiplier-tolerance. 5-band: three digits, then multiplier, then tolerance. 6-band adds a temperature-coefficient band (ppm/K). First band is never black, gold, or silver.
Color code chart
| Color | Digit | Multiplier | Tolerance | Temp coeff. |
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Wire Size & Ampacity Reference
Copper conductor data from NEC Table 310.16 (2023 ed., 30 °C ambient, ≤3 conductors). Enter a load current for a minimum-size recommendation.
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- Cross-section
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- Diameter
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- 60 / 75 / 90 °C
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- Breaker limit*
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*NEC 240.4(D) small-conductor rule: 14 AWG → max 15 A, 12 AWG → max 20 A, 10 AWG → max 30 A breaker, regardless of the temperature column. This table is a reference — derating for ambient temperature, conduit fill, and voltage drop can require larger wire. For educational use — consult a licensed electrician for real wiring work.
Full ampacity table (copper)
| AWG | mm² | Ø mm | 60 °C | 75 °C | 90 °C | Max breaker* |
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Source: NFPA 70 (NEC) Table 310.16, copper conductors. Values are base ampacities before correction/adjustment factors.
Methodology & Worked Examples
How this hub works
Every conversion is a scale factor to the SI base unit: result = value × (from-factor ÷ to-factor). The Ohm's law solver normalizes all inputs (kV, mA, kΩ, MW…) to volts, amps, ohms, and watts before solving, then formats results with SI prefixes. Resistor decoding follows IEC 60062; wire data is NEC Table 310.16 copper at 30 °C ambient. Unlike single-conversion pages, this hub covers the whole electrical-basics domain in one place: units, Ohm's law, power & energy, resistor codes, and wire sizing.
Worked example 1 — LED resistor (Ohm's law in practice)
A 9 V battery must drive a 2 V LED at 20 mA. The resistor drops the remaining 7 V:
R = (Vsupply − Vled) ÷ I
= (9 − 2) ÷ 0.02
= 350 Ω → use the 360 Ω standard value
P = I² × R = 0.02² × 360 = 0.144 W → a ¼ W resistor is safe
Worked example 2 — Heater current & running cost
A 1500 W space heater on a 240 V supply, run 2 hours at $0.15/kWh:
I = P ÷ V = 1500 ÷ 240 = 6.25 A
Energy = 1500 W × 2 h ÷ 1000 = 3 kWh
Cost = 3 × $0.15 = $0.45
Worked example 3 — Reading a resistor
Bands brown – black – red – gold:
digits: brown=1, black=0 → 10
multiplier: red = ×100 → 10 × 100 = 1000 Ω = 1 kΩ
tolerance: gold = ±5% → actual value between 950 Ω and 1050 Ω
Quick reference — common conversions
| From | To | Multiply by |
|---|---|---|
| millivolts (mV) | volts (V) | ÷ 1000 |
| kilovolts (kV) | volts (V) | × 1000 |
| milliamps (mA) | amps (A) | ÷ 1000 |
| kilo-ohms (kΩ) | ohms (Ω) | × 1000 |
| mega-ohms (MΩ) | kilo-ohms (kΩ) | × 1000 |
| microfarads (µF) | nanofarads (nF) | × 1000 |
| nanofarads (nF) | picofarads (pF) | × 1000 |
| millihenries (mH) | henries (H) | ÷ 1000 |
Frequently Asked Questions
16 answers covering Ohm's law, unit conversions, resistor codes, kWh, and wire sizing.
What is Ohm's law?
Ohm's law states that the current (I) through a conductor is directly proportional to the voltage (V) across it and inversely proportional to its resistance (R): V = I × R. From this one equation you can derive every other form: I = V ÷ R, R = V ÷ I, and the power relations P = V × I = I² × R = V² ÷ R. Enter any two of voltage, current, resistance, or power in the Ohm's law calculator above and it solves the other two.
How do I convert volts to amps?
Volts and amps measure different things, so you cannot convert directly — you also need watts or ohms. With power: I = P ÷ V (e.g. a 1200 W appliance at 120 V draws 10 A). With resistance: I = V ÷ R (e.g. 12 V across 4 Ω gives 3 A). Use the Ohm's law calculator above and fill in the two values you know.
How do I convert amps to volts?
Use V = I × R when you know the resistance, or V = P ÷ I when you know the power. For example, 2 A through a 6 Ω load means 12 V across it, and a 240 W device drawing 2 A runs at 120 V.
How do I convert amps to watts, and watts to amps?
Power is voltage times current: P = V × I, so I = P ÷ V. How many amps is 1000 watts? At 120 V it is 8.33 A; at 240 V it is 4.17 A; at 12 V it is 83.3 A — the voltage matters. Conversely, 3 A at 120 V is 360 W.
What is the Ohm's law triangle and the power triangle?
The Ohm's law triangle has V on top with I and R at the bottom: cover the quantity you want and the triangle shows the formula (V = I × R, I = V ÷ R, R = V ÷ I). The power triangle works the same way with P on top and V and I at the bottom (P = V × I, V = P ÷ I, I = P ÷ V). The interactive triangle in the Ohm's law tab highlights whichever pair you entered.
How do I convert mV to V, or kV to V?
Divide millivolts by 1000 to get volts (1000 mV = 1 V) and multiply kilovolts by 1000 (2.2 kV = 2200 V). The quick converter handles every prefix automatically: µV, mV, V, kV, MV for voltage; µA, mA, A, kA for current; and the same ladder for ohms, farads, henries, and siemens.
How do I read resistor color codes?
Resistors follow IEC 60062: each color is a digit (black=0, brown=1, red=2, orange=3, yellow=4, green=5, blue=6, violet=7, gray=8, white=9). Orient the resistor so the gold or silver tolerance band is on the right, then read left to right. For example, brown-black-red-gold is 10 × 100 = 1 kΩ with ±5% tolerance. Select the band colors in the resistor tab to decode any 4, 5, or 6-band resistor.
What is the difference between 4-band and 5-band resistors?
A 4-band resistor uses two significant digits plus a multiplier and a tolerance band (e.g. yellow-violet-red-gold = 4.7 kΩ ±5%) — the standard for general-purpose parts. A 5-band resistor adds a third significant digit for precision parts (e.g. brown-black-black-red-brown = 10 kΩ ±1%). A 6-band resistor adds a temperature-coefficient band in ppm/K.
What is the color code for a 10k resistor?
For a 4-band 10 kΩ resistor: brown (1), black (0), orange (×1 kΩ), then the tolerance band (gold = ±5%). For a 5-band 10 kΩ ±1% resistor: brown, black, black, red (×100 Ω), brown (±1%). The first three bands are always brown-black-orange on a 4-band part.
What is the difference between kW and kWh?
A kilowatt (kW) is power — the rate of energy use right now. A kilowatt-hour (kWh) is energy — power sustained over time, and it is what your electricity bill charges for. A 1.5 kW heater running for 2 hours uses 3 kWh. The power & energy tab computes kWh from watts and hours, plus the cost at your tariff.
What is ampacity, and where do the wire sizes come from?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. The wire reference table uses copper conductor data from NEC Table 310.16 (2023 edition) at 30 °C ambient: for example, 14 AWG = 15/20/25 A, 12 AWG = 20/25/30 A, 10 AWG = 30/35/40 A at 60/75/90 °C columns. Small conductors are additionally limited by NEC 240.4(D): 14 AWG to 15 A, 12 AWG to 20 A, 10 AWG to 30 A.
What size wire do I need for 20 amps? For 30 amps?
For a 20 A circuit, use 12 AWG copper minimum; for 30 A, use 10 AWG copper minimum (per NEC 240.4(D) small-conductor limits). These are minimums — longer runs, hot environments, or more than three conductors in a conduit require larger wire. Enter your load current in the wire-size picker above for a recommendation, and always confirm with a licensed electrician.
Can I use this for AC mains or three-phase conversions?
The Ohm's law and power formulas here assume resistive DC loads (power factor = 1). For single-phase AC with reactive loads, current is I = P ÷ (V × PF); for three-phase, I = P ÷ (√3 × V × PF). A motor with a 0.8 power factor draws 25% more current than the DC formula suggests, so size breakers and wire for the real current, not the idealized one.
Is it safe to use these calculations for real wiring work?
This tool is for educational and reference use. Real installations must follow your local electrical code, account for derating (ambient temperature, conduit fill, voltage drop over distance), and be done or verified by a licensed electrician. Undersized wire overheats and is a fire hazard — when in doubt, go one size larger and get professional confirmation.
Do my numbers leave my browser?
No. This page is a single self-contained file with zero network requests: no analytics, no fonts, no APIs. Every calculation runs locally in your browser via JavaScript, and nothing you type is transmitted anywhere. You can verify this in your browser's developer tools network panel.
Which units does the electrical converter support?
Voltage (µV, mV, V, kV, MV), current (µA, mA, A, kA), resistance (mΩ, Ω, kΩ, MΩ), capacitance (pF, nF, µF, mF, F), inductance (nH, µH, mH, H), and conductance (µS, mS, S). The Ohm's law solver additionally accepts kV, mA, kΩ, MΩ, mW, kW, and MW inputs and normalizes everything to SI base units before solving.
🔒 Private by design. This page is a single self-contained file with zero network requests — no analytics, no fonts, no APIs. All calculations run locally in your browser; nothing you type ever leaves your device.
Educational / reference use only. Real electrical installations must follow your local electrical code and be done or verified by a licensed electrician. Undersized wire and overloaded circuits are fire hazards.