Set your multimeter to measure amps before touching any circuit
To check amps with a multimeter, you need to switch the dial to the amperage setting, insert the red probe into the amp jack (not the voltage jack), and connect the multimeter in series with the circuit — meaning the current flows through the meter itself, not around it. This is different from measuring voltage, where the meter sits in parallel across a component. Breaking the circuit to insert the meter is the key step most people miss.
The meter will show you the current flowing through whatever you are testing. If you are checking whether a device is drawing the expected amount of power, or whether a wire is carrying too much current, the amp reading tells you that. Most household circuits and small devices draw milliamps (mA) or amps (A), and your multimeter will have separate jacks and dial settings for each range.
Key Takeaways
- Insert the red probe into the amp jack on your multimeter, not the voltage jack, before you start measuring.
- Connect the multimeter in series with the circuit by breaking the connection and letting current flow through the meter itself.
- Start with the highest amp range on the dial and work downward to find the right setting without damaging the meter.
- If the reading shows 0 or OL (overload), switch to a lower or higher range until you get a stable number on the display.
Understand the difference between series and parallel connection
When you measure amps, the multimeter must be in series with the circuit. That means you physically break the circuit at one point, and the current flows into the meter through one probe and out through the other. The meter sits in the path of the electricity, not off to the side.
This is the opposite of measuring voltage, where you touch the probes across a component without breaking anything. If you try to measure amps in parallel — by touching the probes across a wire or component without breaking the circuit — you will short-circuit the meter and likely damage it. The meter has almost no resistance, so current will flood through it instead of through the rest of the circuit.
To put the meter in series, you need to physically disconnect one end of a wire, remove a component from its socket, or break a connection at a solder joint. Then connect one probe to the disconnected end and the other probe to the other side of the break. Current now flows through the meter to complete the circuit.
Choose the right jack and dial range before connecting
Multimeters have three jacks: one for the black probe (ground), one for the red probe when measuring voltage or resistance, and one for the red probe when measuring amps. The amp jack is usually labeled with an A or mA and is separate from the voltage jack. If you plug the red probe into the wrong jack, you will not measure amps at all.
Once the red probe is in the amp jack, turn the dial to the amp setting. Most multimeters have two amp ranges: milliamps (mA) for small currents and amps (A) for larger ones. Start with the highest range — usually 10A or 20A — to avoid blowing the meter's internal fuse. If the reading is very small or shows 0, switch down to the milliamp range. If it shows OL (overload), you have exceeded that range and need to go back up.
Some multimeters have a separate dial position for DC amps and AC amps. Check whether you are measuring direct current (DC) from a battery or power supply, or alternating current (AC) from a wall outlet or transformer. Choosing the wrong one will give you an incorrect reading or no reading at all.
Connect the meter in series and read the display
Locate the point in the circuit where you want to measure current. This might be a wire leading to a device, a component in a breadboard, or a connection on a circuit board. Disconnect one end of that wire or component so the circuit is broken and no current flows.
Touch the black probe to one side of the break and the red probe to the other side. Current will now flow through the meter. The display will show the current in amps or milliamps. If the number is stable, you have the right range. If it shows 0, the circuit may not be powered on, or you may need to switch to a lower range. If it shows OL, the current exceeds that range and you need to switch to a higher one.
Once you have your reading, disconnect the probes and reconnect the wire or component to restore the circuit. Do not leave the meter in series any longer than necessary, because you are interrupting the normal operation of the device.
Protect the meter by starting high and working down
The most common mistake is starting with a low amp range on a circuit that draws high current. If you select 200mA and the circuit draws 2 amps, you will blow the meter's internal fuse instantly. The fuse is there to protect the meter, but once it blows, you cannot measure amps until you replace it.
Always start with the highest range available — usually 10A or 20A — even if you expect the current to be small. Take a reading. If the number is very low or shows 0, switch down one range at a time until you get a stable reading in the middle of the display. This way, you will never exceed the meter's limit.
If you do blow the fuse, the meter will show 0 on every amp measurement no matter what you connect. You will need to open the meter's battery compartment, locate the fuse (usually a small cylinder near the jacks), and replace it with one of the same amperage rating. The rating is printed on the fuse itself and in the meter's manual.
Common problems and what they mean
If the meter shows 0 amps when you expect current to flow, first check that the circuit is actually powered on. Then verify that you have the red probe in the amp jack, not the voltage jack. If both are correct, try switching to a lower range — the current may be too small for the range you selected. If you still see 0 on the lowest range, the circuit may be broken or the meter's fuse may be blown.
If the meter shows OL (overload), the current exceeds the range you selected. Switch to a higher range immediately. If the highest range also shows OL, the current is too large for your meter to measure safely. Do not attempt to measure it; you risk damaging the meter or creating a fire hazard.
If the reading bounces or changes rapidly, the connection may be loose or the circuit may be unstable. Wiggle the probes slightly to ensure good contact. If the reading still jumps, the device itself may be drawing variable current, which is normal for some equipment like motors or power supplies.
Frequently Asked Questions
Can I measure amps without breaking the circuit?
No. Measuring amps requires the meter to be in series, which means breaking the circuit and letting current flow through the meter. If you try to measure amps in parallel by touching the probes across a wire, you will short-circuit the meter and damage it. Always disconnect one end of the wire or component first.
What is the difference between amps and milliamps?
One amp equals 1,000 milliamps. Milliamps (mA) are used for small currents like those in LED circuits or phone chargers. Amps (A) are used for larger currents like those in household appliances or car batteries. Your multimeter has separate jacks and dial settings for each, so choose the right one for the current you expect.
What happens if I measure amps with the probes in the voltage jack?
The meter will not measure amps at all. You will see 0 or an error on the display. The amp jack and voltage jack are separate, so the red probe must go into the amp jack before you start. Check the labels on your meter to find the correct jack.
How do I know if I blew the fuse?
If the meter shows 0 amps on every measurement, even on the highest range, the fuse is likely blown. Open the battery compartment, find the fuse (a small cylinder near the jacks), and replace it with one of the same amperage rating. The rating is printed on the fuse and in the meter's manual.
Can I measure AC amps the same way as DC amps?
The connection method is the same — series, with the meter in the path of the current — but you must select the AC amp setting on the dial instead of DC. Using the wrong setting will give you an incorrect reading. Check whether your circuit is powered by a battery (DC) or a wall outlet (AC) before you measure.