Volts to mA Converter
A 5 V supply across a 1,000 ohm resistor pushes 5 mA, a small current of the kind a status light uses.
Quick answer: Divide the voltage by the resistance in ohms, then multiply by 1,000. For example, 5 V across 1,000 Ω is 5 mA, 12 V across 470 Ω is 25.532 mA and 3.3 V across 220 Ω is 15 mA.
The volts to mA formula
Current in amps equals voltage divided by resistance. This is Ohm law (Skill-Lync Resources: Ohm Law Calculator).
Multiply the amps by 1,000 to get milliamps. You cannot convert volts to mA without knowing the resistance.
Take 5 V across 1,000 Ω. 5 ÷ 1,000 × 1,000 gives 5 mA.
Take 12 V across 470 Ω. 12 ÷ 470 × 1,000 gives 25.532 mA.
Volts, ohms and milliamps
Volts are the push. Ohms are how hard the circuit resists that push. The current is how much actually flows.
A milliamp is one thousandth of an amp. Small circuits and sensors are usually measured in milliamps.
How to convert volts to mA step by step
- Enter the voltage across the resistance.
- Enter the resistance in ohms.
- Divide the volts by the ohms to get amps.
- Multiply by 1,000 to get milliamps.
Example 1: 5 V across 1,000 Ω
- Start with 5 V across 1,000 Ω.
- 5 ÷ 1,000 × 1,000 = 5.
- The current is 5 mA.
5 V across 1,000 Ω = 5 mA
Example 2: 12 V across 470 Ω
- Start with 12 V across 470 Ω.
- 12 ÷ 470 × 1,000 = 25.532.
- The current is 25.532 mA.
12 V across 470 Ω = 25.532 mA
Example 3: 3.3 V across 220 Ω
- Start with 3.3 V across 220 Ω.
- 3.3 ÷ 220 × 1,000 = 15.
- The current is 15 mA.
3.3 V across 220 Ω = 15 mA
Use the voltage that is actually across the resistor. If other parts share the supply, the resistor sees less than the full supply voltage.
volts to mA conversion table
| Voltage and resistance | Current | In amps |
|---|---|---|
| 1.5 V across 100 Ω | 15 mA | 0.015 A |
| 3.3 V across 220 Ω | 15 mA | 0.015 A |
| 5 V across 330 Ω | 15.152 mA | 0.0152 A |
| 5 V across 1,000 Ω | 5 mA | 0.005 A |
| 5 V across 10,000 Ω | 0.5 mA | 0.0005 A |
| 9 V across 470 Ω | 19.149 mA | 0.0191 A |
| 12 V across 470 Ω | 25.532 mA | 0.0255 A |
| 12 V across 1,000 Ω | 12 mA | 0.012 A |
| 24 V across 4,700 Ω | 5.106 mA | 0.005106 A |
| 230 V across 10,000 Ω | 23 mA | 0.023 A |
The highlighted row is the default of the calculator. The last column gives A.
A quick mental shortcut for volts to mA
Divide the volts by the kilo-ohms to get milliamps directly. 5 V across 1 kΩ is 5 mA.
12 V across 470 Ω is about 25 mA.
Milliamps and amps
One amp is 1,000 milliamps. So 0.005 A is 5 mA, and 0.25 A is 250 mA.
Always write the unit. A bare 5 could mean amps or milliamps.
An LED resistor example
An LED on a 5 V supply may drop about 2 V. The resistor then sees 3 V, and with 330 ohms the current is 9.0909 mA.
The 2 V drop is a typical value. Check the data sheet of your LED.
Power in the resistor
The power in a resistor equals volts squared divided by ohms. For 5 V across 1,000 ohms that is 25 mW (Skill-Lync Resources: Ohm Law Calculator).
Choose a resistor rated well above that, so it stays cool.
Kilo-ohms make it easy
When the resistance is in kilo-ohms, volts divided by kilo-ohms gives milliamps directly. 12 V across 4.7 kΩ is 2.5532 mA.
This shortcut avoids a factor of 1,000 mistake.
Meter ranges and fuses
A meter has separate ranges for milliamps and amps. Put the lead in the correct socket before you measure a current.
A small mA range may be protected by a small fuse, which can blow if you try to read a large current.
Going the other way
To get the resistance, divide the voltage by the current in amps.
For 5 V and 5 mA, the resistance is 1,000 ohms.
Check your answer
Multiply your milliamps by the resistance and divide by 1,000. You should get the voltage back.
For 25.5 mA across 470 ohms the result is about 12 V, which matches.
Quick conversion answers
| Conversion | Result |
|---|---|
| 3 V across 150 Ω | 20 mA |
| 5 V across 220 Ω | 22.727 mA |
| 6 V across 1,200 Ω | 5 mA |
| 9 V across 2,200 Ω | 4.091 mA |
| 12 V across 330 Ω | 36.364 mA |
| 24 V across 1,000 Ω | 24 mA |
Where this conversion is used
Hobbyists work out how much current an LED or a sensor draws.
Technicians check that a circuit stays within the current limit of a part.
Students practise Ohm law with real component values.
Common mistakes to avoid
- Forgetting to multiply by 1,000. 5 V across 1,000 ohms is 0.005 A, which is 5 mA, not 5 A.
- Using the supply voltage across a part that shares it. Use the voltage across the resistor only.
- Mixing kilo-ohms and ohms. 1 kΩ is 1,000 Ω. Entering 1 makes the current 1,000 times too big.
- Ignoring resistor tolerance. A 5 percent resistor can change the current by about 5 percent.
Related converters
Frequently asked questions
How do I convert volts to mA?
Divide the volts by the ohms, then multiply by 1,000.
Can I convert volts to mA without resistance?
No. You also need the resistance or the power.
How many mA is 5 V across 1,000 ohms?
It is 5 mA.
How do I turn amps into mA?
Multiply by 1,000.
What is Ohm law?
Voltage equals current times resistance.
How do I find the resistor power?
Divide the voltage squared by the resistance.
Sources
- Skill-Lync Resources: Ohm Law Calculator (resources.skill-lync.com)
- Wikipedia: Watt (en.wikipedia.org)
