There's a quiet snobbery about this. "Real musicians tune by ear," says someone's uncle, while a violinist with thirty years of ear training checks her A against a tuner anyway. The truth is less romantic: a tuner is more accurate than any human ear, and ear tuning makes you a better musician. These are different facts. You want both.
A tuner reads a clean string to better than one cent. Trained ears notice around five. But the tuner only works when you're holding it — your ears come to rehearsal, hear that your B string drifted mid-song, and fix it between phrases. That skill is built, not born, and tuning by ear daily is how it's built.
The classic, using the guitar against itself. Get the low E right first — from the pitch pipe, the tuner, or any note you trust. Then:
1 – Fret the low E at the 5th fret. That's an A. Pluck it and the open A string together and listen — not for "same note", but for beating: a slow wah-wah-wah pulse when two pitches are close but not equal.
2 – Turn the A peg until the beating slows… slows… stops. That silence between the notes is "in tune". It's a physical thing, not a judgment call, which is what makes this learnable.
3 – Repeat down the set: A 5th fret → D, D 5th fret → G, then G 4th fret → B (the one exception everyone forgets), B 5th fret → high E.
The catch: errors stack. Each pair you tune inherits the error of the one before, so by the high E you can be audibly off even though every step sounded fine. It's a fine method; it's just five approximations standing on each other's shoulders.
Touch the low E lightly right above the 5th fret wire (don't press) and pluck: a chime, two octaves up. Touch the A string at its 7th fret: nearly the same pitch. Sound both and tune out the beats. Harmonics ring long after your hand leaves, so both notes sustain while you turn the peg — easier than the fretted version, and no fretting-hand pressure to skew the pitch.
Small honesty note: the 7th-fret harmonic is mathematically a hair flat of equal temperament (two cents). For song-level tuning, ignore this. For impressing physicists, mention it.
Because beat-listening is intonation training in disguise. String players who practice against a drone develop the same skill — hearing "in tune" as stillness rather than as a needle position. Singers too. Ten minutes a week of ear tuning compounds into hearing your own instrument drift while playing, which no tuner in your pocket can do.
The workflow that trains you fastest: tune by ear first, then open the tuner and grade yourself. Under ten cents of error across the set? Your ears are coming along nicely. The strobe view is strict enough to humble anyone — which is, of course, the fun of it.