A plug-in tester with three lights gives you a quick verdict, but a multimeter gives you numbers, and numbers catch problems a tester waves through — voltage that's sagging, a ground that's present but weak, a neutral that's floating. The test takes two minutes per outlet once you've done it once.
| Measurement | Probes | Healthy reading |
|---|---|---|
| Hot to neutral | Short slot → tall slot | About 120 V (roughly 114–126 is normal) |
| Hot to ground | Short slot → round/U-shaped hole | About 120 V, matching the first reading |
| Neutral to ground | Tall slot → round/U-shaped hole | 0–2 V |
On a standard outlet, the shorter slot is hot, the taller slot is neutral, and the U-shaped hole is ground. Everything below is comparing those three numbers against each other.
Set the meter. Plug the black lead into COM and the red lead into the VΩ jack. Turn the dial to AC voltage (marked V~ or VAC). On a manual-range meter, pick the range above 120 — usually 200 or 600. Auto-ranging meters just need the V~ setting.
Prove the meter on a known-live outlet. Test an outlet you know works and confirm you see roughly 120 V. This is the step beginners skip and the one that matters: a meter with a dead fuse or a lead in the wrong jack reads zero everywhere, and "zero everywhere" sends you hunting for a wiring fault that doesn't exist.
Measure hot to neutral. Black probe in the tall (neutral) slot, red probe in the short (hot) slot. Steady the probes — the reading will jump around until both make solid contact. You want about 120 V.
Measure hot to ground. Leave the red probe in the hot slot and move the black probe to the ground hole. A healthy outlet repeats the same ~120 V. This reading is also how you confirm an outlet is actually grounded with a meter — the full method is in our guide on how to tell if an outlet is grounded.
Measure neutral to ground. Black probe to ground, red probe to the neutral slot. Expect near zero — a volt or two under load elsewhere in the house is unremarkable. Anything well above that means neutral and ground aren't meeting where they should.
Re-prove the meter. Back to the known-live outlet, confirm ~120 V again. Now a zero reading on the problem outlet is a fact, not a meter failure.
| Pattern (H-N / H-G / N-G) | Likely problem | What to do |
|---|---|---|
| 120 / 120 / ~0 | None — wired correctly | Done |
| 0 / 0 / 0 | No power: tripped breaker, tripped GFCI upstream, or a switch-controlled outlet | Check the panel for a tripped breaker and reset any GFCI outlets on the circuit, then retest |
| 120 / 0 or erratic / 0 or erratic | Open ground | The outlet works but has no safety ground. Common in older homes; an electrician can add grounding or GFCI protection |
| 120 / ~0 / ~120 | Reversed polarity (hot and neutral swapped) | Stop using sensitive electronics there; the receptacle needs its connections corrected |
| 0 / 120 / 0 | Open neutral | Power reaches the outlet but can't complete the circuit. Electrician territory — don't keep plugging things in to test |
| Well under 110 / matching / low | Voltage drop: loose connection or overloaded circuit | Treat as a heating risk at the loose point; get it traced rather than living with it |
One wrinkle: a digital meter can show a "ghost" reading — 40, 70, 90 volts — on a wire or outlet that isn't actually powered. Digital meters draw almost no current, so stray induced voltage from neighboring live wires doesn't bleed off. If a reading looks like a fraction of 120 and the outlet runs nothing, confirm with the plug-in tester or by testing under a real load before you conclude anything.
Leaving the dial on ohms or DC. Measuring resistance on a live circuit can destroy the meter in a flash of sparks, and DC volts on an AC outlet just reads near zero and sends you chasing a fault that isn't there. Check the dial out loud before the probes touch the slots.
Gripping the probe shafts. Fingers belong on the insulated handles, behind the finger guards. Slipping off a slot contact is easy; the guard is what keeps your hand out of the slot when it happens.
Assuming a dead reading means it's safe to open the box. It doesn't. A receptacle can be fed from more than one direction, switches confuse things, and your meter only proved the face wasn't live at that moment. Testing is a face-level job; opening boxes is a different job with its own rules.
Three readings — hot-neutral, hot-ground, neutral-ground — turn "the outlet seems dead" into a diagnosis. About 120, the same 120, and near zero is a healthy outlet; every other pattern points at a specific fault from the table. If the same wrong pattern shows up on outlet after outlet, you're not looking at one bad receptacle anymore — work through the signs your house needs rewiring before you spend money one device at a time.
Around 120 volts between hot and neutral. Utilities deliver within a tolerance band, so anything roughly between 114 and 126 volts is ordinary. Readings a few volts lower under heavy load elsewhere in the house are also common; a big, persistent drop is the thing worth investigating.
Most often that's a ghost voltage — a digital meter picking up induced voltage on a disconnected or open wire, not real power. A plug-in tester or any actual load will collapse it to zero. If the outlet does run a lamp but the voltage stays low, that's a genuine voltage drop, usually a loose connection, and it deserves a real look.
Yes. If hot-to-ground reads the same ~120 volts as hot-to-neutral, a ground path exists. If hot-to-neutral is 120 but hot-to-ground reads zero or wanders, the ground is open. Note the meter confirms the path exists at that moment — it can't certify the ground is in good condition all the way back to the panel.
For a fast polarity-and-ground check, it's genuinely handy and takes five seconds. What it can't do is give you numbers: it won't show voltage sag, a neutral-to-ground problem developing, or the difference between 108 and 122 volts. Plenty of homeowners own both and use the tester first, meter second.
Check for a tripped GFCI upstream — one GFCI receptacle often protects several plain outlets downstream, in bathrooms, kitchens, garages, and outside. Then check whether the outlet is controlled by a wall switch (common in living rooms and bedrooms). If neither explains it, the receptacle or a connection has failed, and that's the point to bring in an electrician rather than open boxes yourself.