An 1:10 voltage divider for your ADC consists of two resistors, one having a R value and the other a 9R value.
The problem is that no pair of the common E12 E24 standardized resistor value pairs can provide the perfect ratio 1:9.

Resistors are usually cheap, so the first idea is to puchase exactly 10 resistors. This has the following advantage: the resistors purchased on a reel are usually from the same batch, so their value match better together.

But you can do the same with only 6 resistors:

|-----RRRR-----|
|-----RRRR-----|----RRRR--------RRRR--------RRRR----|
|-----RRRR-----|

between 0V and the ADC you have 3 resistors in // so the corresponding value is R/3
between the ADC have 3 resitors in serie so the corresponding value is 3R.

3R / (R/3) = 9 the perfect ratio required!

You may use any R value between 1K and 50K

Enjoy!

RIN67630:
The problem is that no pair of the common E12 E24 standardized resistor value pairs can provide the perfect ratio / (R/3) = 9 the perfect ratio required!

Three resistors can. Two 18k in parallel, and one 1k to ground.

But why the "perfect ratio".
An Arduino hasn't got a "perfect Aref", so you always need to calibrate anyway.
Leo..

And there is always a 10 turn potentiometer.

.

"An Arduino hasn't got a "perfect Aref","
So an external reference driving Aref is needed.

Use one these to get a very stable, accurate 4.096V or 4.5V from the USB supply.
https://www.digikey.com/products/en/integrated-circuits-ics/pmic-voltage-reference/693?k=ref194

Hi,
I used the MCP1541. Since it is a TO92 you can easily mounting it in the Arduino board.