SMD Resistors - Typical Power Ratings

According to Google:

Package style Typical Power Rating (W)

1206 1/8 W

0805 1/10 W

0603 1/16 W

Standard Resistor/Capacitor Series

If you are buying a Resistor Kit then get E12

If you are buying an 0.1uF and larger Capacitor Kit then get E6

If you are buying an pF and nF Capacitor Kit then get E12

E6 -

1.0 1.5 2.2

3.3 4.7 6.8

E12 -

1.0 1.2 1.5

1.8 2.2 2.7

3.3 3.9 4.7

5.6 6.8 8.2

E24 -

1.0 1.1 1.2

1.3 1.5 1.6

1.8 2.0 2.2

2.4 2.7 3.0

3.3 3.6 3.9

4.3 4.7 5.1

5.6 6.2 6.8

7.5 8.2 9.1

There is no simple way of guessing voltage ratings of SMD Capacitors from their physical size and measured capacitance as the voltage rating varies significantly by the dielectric used by the manufacturer.

The above graph is from
https://electronics.stackexchange.com/questions/364522/smd-ceramic-capacitor-mlcc-0805-vs-0603

As you can see a 3uF 0805 capacitor can be rated for use with 3.3V or 5V so may not be safe to use in 5V circuits

So when using a recovered capacitor it is best to measure the voltage in circuit before taking it off the donor board.