Most ukulele players learn songs from chord sheets and tabs. There is nothing wrong with that. But once you can learn a song by ear, your relationship with music changes. You stop needing permission to play. You hear something, you pick it up. That skill is learnable - it is not reserved for people with perfect pitch.
This is a method, not a mystery. Work through it slowly and it becomes reliable.
Step 1: Find the Key
Play a low note on your ukulele while the song plays. Move up one fret at a time on the C string until the note feels like it belongs. That note - the one that sounds like home when the song is playing - is probably the root of the key.
On ukulele, try the C string (third string) frets 0-5. Once the root feels settled, you know you are in the right neighbourhood. If the root note is on fret 2, you are probably in D major or B minor.
Step 2: Try the Four Most Common Chords
Most popular songs use four chords. In any major key, those are the I, IV, V, and vi chords. If the song is in C major, those are C, F, G, and Am. If it is in G major: G, C, D, Em.
CF
Start with the I chord (the root). Strum it while the song plays and check whether it fits. Then try the vi (the relative minor, which is Am in the key of C). Most songs start on I or vi and move through the others. Once you find two chords that fit, the other two usually follow quickly.
Step 3: Listen for Chord Changes
Chord changes almost always happen on beat 1 of a bar, or on beat 3 in a 4/4 song. Listen for the moment the song's harmony shifts - there is often a slight emphasis or a change in the bass note. Tap your foot and count bars. Play the chord you have, wait for a shift, then try the next candidate.
Do not try to figure out every chord change in one pass. Loop the first four bars. Get those right. Then move to bars five through eight.
Step 4: Check Against the Bass
When you are unsure which chord is playing, listen to the lowest note in the recording. That bass note is usually the root of the chord. Hum it and then find it on your C or G string. That narrows your options considerably.
Step 5: Confirm by Playing Along
Once you have a rough chord map, play the whole song through with the recording at low volume. Wrong chords sound unmistakably wrong - trust that feeling. Right chords create a sense of release or resolution. Adjust until each transition feels settled rather than tense.
Practice Exercise
Pick a song you know well enough to hum the melody. Not a song you have looked up - one you already carry in your head. Songs you know deeply are much easier to decode because you already hear all the parts.
Find the root note on your C string
Identify the key (major or minor feel?)
Try I, IV, V, vi in that key over the song
Adjust any chord that sounds wrong
Play the full song through from start to finish
It will take longer the first time. The fifth time it will be faster. The twentieth time it will feel automatic.
Questions and Answers
How do you find the key of a song by ear on ukulele?
Play along with the song and find the note that sounds most settled when the song is at rest - this is the root note of the key. On ukulele, try notes on the C string while the song plays and stop when one feels like home. The most common keys for ukulele are C, G, F, D, and A major.
What chords should you try first when learning a song by ear?
Start with the four chords most common in popular music: the I, IV, V, and vi chords of the key. In C major these are C, F, G, and Am. Most songs can be approximated with these four chords before any other chords are considered.
Next up: Simple Songwriting - once you can decode songs, writing your own is the natural next step.