A 12 fl oz can of Coca-Cola Classic has 34 mg of caffeine. The same size can of Pepsi has 38 mg - 4 mg more. Both are modest next to a cup of coffee; the gap between these two colas is small enough that it rarely matters for your daily total on its own.

Figures are each company's own published data; see the source link in the table below. Add either one to the caffeine calculator to see how it fits your personal daily limit.

Standard can, side by side

Coca-Cola Classic, 12 fl oz (355 ml) 34 mg
Pepsi, 12 fl oz (355 ml) 38 mg

Sources

Drink Serving Caffeine Source
Pepsi 12 fl oz (355 ml) 38 mg PepsiCo Product FactsSource
Coca-Cola Classic 12 fl oz (355 ml) 34 mg The Coca-Cola Company, ingredients FAQSource