When reading schematics, building or repairing amplifiers and also buying capacitors, you often must convert between uF, nF and pF.

Paper, plastic and electrolytic capacitors are usually expressed in terms of uF (microfarads). Short forms for micro farad include uF, mfd, MFD, MF and UF.

Mica capacitors are usually expressed in terms of pF (micromicrofarads) (picofarads).
Short forms for micromicrofarads include pF, mmfd, MMFD, MMF, uuF and PF. A pF is one-millionth of a uF.

In between a pF and a uF is a nF which is one-one thousands of a uF. Converting back and forth between uF, nF  and pF can be confusing with all those darn decimal points to worry about. Below is a uF - nF- pF conversion chart.
Just print a copy and tape it to your workbench….it will come in handy.

Here is a great site with a lot of information about replacing and identifying capacitors. The site is geared toward old radios but it applies directly to tube guitar amps. Phil’s Old  Radios.

  Capacitor Reference Chart

Here is a chart with the old style color codes on capacitors.