This link could be helpful.

"Molarity Calculator & Normality Calculator for Acids & Bases | Sigma-Aldrich" https://www.sigmaaldrich.com/chemistry/stockroom-reagents/learning-center/technical-library/molarity-calculator.html

I. On pH prediction for (pure) KOH aq. sol.:

The following pH prediction for KOH aq. sol. takes into account the hydrolysis equilibrium of the K+ cation:

The pH of KOH aq. sol. can be predicted from the hydrolysis constant (Kh = 3.2·10-15 M) (*) of K+ for the equilibrium: K+ + 2 H2O ⇌ KOH + H3O+; Kh = [KOH]·[H3O+]/[K+]. We can substitute [KOH] at previous equation based on charge balance and molar balance for potassium, respectively:

[K+] = [OH-] - [H3O+] = Kw/[H3O+] - [H3O+], [KOH] = CKOH - [K+] = CKOH - [OH-] + [H3O+] = CKOH - Kw/[H3O+] + [H3O+], where Kw is autodissociation constant of water (Kw = 1.0·10-14; units omitted) and CKOH is the nominal molar concentration of dissolved KOH (formality, to be precise).

Hence we can write: Kh = {CKOH - Kw/[H3O+] + [H3O+]}·[H3O+]/{Kw/[H3O+] - [H3O+]} = {{[H3O+] + CKOH}·[H3O+] - Kw}·[H3O+] /{Kw - [H3O+]2}.

As long as CKOH > 100·[H3O+] and CKOH > 100·Kh, this simplifies to:

[H3O+]2 - ½2(Kw /CKOH)·[H3O+] ≈ Kh·Kw/CKOH.

This solves as:

[H3O+] ≈ ½(Kw/CKOH){1 + √{1 + 4CKOH·Kh/Kw}}

With CKOH = 1.00·10-1 M:

[H3O+] ≈ ½((1.00·10-14 M2)/(1.00·10-1 M)){1 + √{1 + 4(1.00·10-1 M)·(3.2·10-15 M)/(1.00·10-14 M2)}} = ½·(1.00 + √1.128)·10-13 M = 1.03·10-13 M; pH = - log10{[H3O+]/M} = 13 - log10(1.03) = 12.99

II. By predicting the pH of (pure) KOH aq. sol. as that of a strong base, we simply have:

[OH-] ≈ CKOH; pOH = - log10{[OH-]/M}

With CKOH = 1.00·10-1 M: pOH = 1.00; pH = 14.00 - pOH = 13.00

Note that for most practical purposes we can consider KOH as the strongest base in water.

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(*) pKa = - log10(Kh) = 14.5: https://www.wou.edu/las/physci/ch412/Table2.htm

III. Please note that the weighted KOH pellets may actually contain more moisture than what might have been accounted for, while both pellets and solution are prone to carbonation when exposed to the atmospheric CO2. Solutions of KOH should be standardized (by titration) for quantitative analytical purposes; so that the actual solution concentration can be determined.

IV. This standard may help: ASTM E291 - 18, "Standard Test Methods for Chemical Analysis of Caustic Soda and Caustic Potash (Sodium Hydroxide and Potassium Hydroxide)"; https://www.astm.org/Standards/E291.htm