What is a fluid ounce?

A fluid ounce (fl oz) measures liquid volume. In the US system, 1 cup = 8 fl oz. Weight ounces (oz) measure mass and vary by ingredient density.

How to convert (step‑by‑step)

1. Identify the unit you have: cups or fl oz.
2. Use the ratio 1 cup = 8 fl oz.
3. Apply the formula:
   • cups → fl oz: fl oz = cups × 8
   • fl oz → cups: cups = fl oz ÷ 8
4. Round as needed for your recipe (2 decimals is usually enough).

Worked examples

• 2 cups → fl oz = 2 × 8 = 16 fl oz
• 12 fl oz → cups = 12 ÷ 8 = 1.5 cups
• 1/3 cup → fl oz = 0.333… × 8 ≈ 2.67 fl oz

Quick reference

• 1/4 cup = 2 fl oz
• 1/3 cup ≈ 2.67 fl oz
• 1/2 cup = 4 fl oz
• 3/4 cup = 6 fl oz
• 1 cup = 8 fl oz

Common mistakes

• Confusing fl oz (volume) with oz (weight)—they are not interchangeable.
• Using metric cup values (250 ml) without converting to fl oz (1 fl oz ≈ 29.57 ml).
• Over‑rounding small fractions—keep 2 decimal places for accuracy.

US vs Metric cups

In US recipes, 1 cup = 8 fl oz. A metric cup = 250 ml, which is about 8.45 fl oz. If your cookware or cookbook is Australian/European, confirm the cup standard before converting.

Liquid vs dry measuring

• Use a clear liquid measuring cup for liquids and read at eye level.
• Use dry measuring cups for flour/sugar and level with a straight edge.
• Tip: For viscous liquids (honey, syrup), lightly oil the cup to release cleanly.

Rounding & precision

For everyday cooking, round to the nearest 0.5 fl oz or to the nearest 1/4 cup. For baking or coffee drinks, keep two decimals (e.g., 2.67 fl oz for 1/3 cup).

Mini conversion list

• 2.5 cups = 20 fl oz
• 16 fl oz = 2 cups
• 10 fl oz = 1.25 cups
• 6 fl oz = 3/4 cup