Decide if your goal is drink-style bitterness (cocktail, spritz, riff) or baking flavor (depth, color, tangy bitterness).
Choose the highest-ranked option that matches your needed intensity; apply using the listed ratio (1:1 unless noted).
If the substitute tastes sweeter or less bitter than Campari, add 2–6 dashes of orange bitters (or a small pinch of bitter herbs in baking).
If the substitute tastes flat or too herbal, add a little fresh orange zest (drinks) or a tiny splash of citrus (baking) to lift the aroma.
Taste and adjust: you should feel bitter-orange character without harshness; keep notes for next time.