Puerto Rican cuatro fret calculator
The cuatro built by Rafael Avilés Vázquez in 1999–2000, now at the Smithsonian's National Museum of American History, has a 51.5 cm scale, and Thomann's Puerto Rico cuatro measures about the same. The calculator starts at 515 mm (20.28″) with 20 frets: the 1st fret sits 28.90 mm from the nut, the 5th 129.19 mm, the 12th 257.50 mm and the 20th 352.79 mm.
Puerto Rican cuatro fret positions, 515 mm scale
Distance of each fret from the nut, from the previous fret and to the saddle on a 20-fret cuatro.
| Fret | From nut (mm) | From previous (mm) | To saddle (mm) |
|---|---|---|---|
| 1 | 28.90 | 28.90 | 486.10 |
| 2 | 56.19 | 27.28 | 458.81 |
| 3 | 81.94 | 25.75 | 433.06 |
| 4 | 106.24 | 24.31 | 408.76 |
| 5 | 129.19 | 22.94 | 385.81 |
| 6 | 150.84 | 21.65 | 364.16 |
| 7 | 171.28 | 20.44 | 343.72 |
| 8 | 190.57 | 19.29 | 324.43 |
| 9 | 208.78 | 18.21 | 306.22 |
| 10 | 225.97 | 17.19 | 289.03 |
| 11 | 242.19 | 16.22 | 272.81 |
| 12 | 257.50 | 15.31 | 257.50 |
| 13 | 271.95 | 14.45 | 243.05 |
| 14 | 285.59 | 13.64 | 229.41 |
| 15 | 298.47 | 12.88 | 216.53 |
| 16 | 310.62 | 12.15 | 204.38 |
| 17 | 322.09 | 11.47 | 192.91 |
| 18 | 332.92 | 10.83 | 182.08 |
| 19 | 343.14 | 10.22 | 171.86 |
| 20 | 352.79 | 9.65 | 162.21 |
Smithsonian NMAH, cuatro by Rafael Avilés Vázquez, 1999–2000 (51.5 cm scale)
How to use it
- Tap PR cuatro 515 mm or type your scale. Measure from the nut to the 12th fret and double it.
- Set the number of frets. Wikipedia gives 18 to 20 for the cuatro, without a source, so count the frets on yours.
- Keep the compensation for wound steel strings: the cuatro's A, E and B courses all carry wound strings.
- Print at 100%, measure the 100 mm bar and tape the sheets on the splice line.
Help and explanations
Type your own scale if your cuatro differs, then print the template at full size to mark a fretboard or check an old one. It runs in your browser, free, with no sign-up.
Scale length of the Puerto Rican cuatro
The modern Puerto Rican cuatro has five double courses of steel strings, ten in all, and a body cut from a single block of wood in the traditional build. Published measurements put the scale around 51 to 51.5 cm: the Avilés Vázquez cuatro at the Smithsonian is 51.5 cm, and an older four-course cuatro antiguo from Ponce in the same collection measures 51 cm.
Don't confuse it with the Venezuelan cuatro, a four-string nylon instrument of a different size and tuning. Since fret positions depend only on the scale, enter the length you measure and the table works for either.
Saddle compensation on a cuatro
Fretting stretches the string and raises its pitch, so the saddle sits a little behind the nominal scale. With plain steel on top and wound strings on the A, E and B courses, the calculator suggests 2.5 to 4 mm as a starting range, labeled as an estimate.
The final check is the octave at the 12th fret, which on a 515 mm scale is at 257.50 mm. Test each string of the octave courses separately with the intonation checker.
Tips
- Mark every fret from the nut, never fret to fret, so small ruler errors don't add up.
- Before you print, check the 100 mm bar: a printer that rescales by 3 % moves the 20th fret by more than 10 mm.
- Tune the five courses with the Puerto Rican cuatro tuner before you check intonation.
Frequently asked questions
What is the scale length of a Puerto Rican cuatro?
About 51.5 cm (20.3″). That's the scale of the Rafael Avilés Vázquez cuatro at the Smithsonian and of Thomann's Puerto Rico cuatro. Measure yours from the nut to the 12th fret and double it.
How many frets does a Puerto Rican cuatro have?
Usually 18 to 20, according to Wikipedia (without a cited source). Count the frets on your instrument and enter that number.
Where is the 12th fret on a 515 mm cuatro?
At 257.50 mm (10.138″) from the nut. The 1st fret is at 28.90 mm, the 5th at 129.19 mm, the 7th at 171.28 mm and the 20th at 352.79 mm.
Is the Puerto Rican cuatro the same as the Venezuelan cuatro?
No. The Puerto Rican cuatro has ten steel strings in five courses, tuned B E A D G; the Venezuelan cuatro has four nylon strings. Their scales differ too, so measure the instrument you have.