How Much Does a Fluid Ounce Weigh in Grams?

1 US fluid ounce (fl oz) of water weighs 29.5735 grams (g), and 1 UK (Imperial) fluid ounce of water weighs 28.4131 grams. The weight changes for other liquids because each liquid has a different density (mass per unit volume).

A fluid ounce is a unit of volume, not weight. The gram weight of a fluid ounce depends on what liquid fills that volume. Water is the baseline reference because water has a density of 1.0 g/mL at 4 °C (39.2 °F).

Weight of 1 Fluid Ounce for 7 Common Liquids

There are 7 liquids most people measure in everyday cooking, baking, and nutrition tracking. The table below lists the weight of 1 US fl oz (29.5735 mL) for each liquid.

Honey weighs 42.01 grams per US fluid ounce — 42% heavier than the same volume of water. Vegetable oil weighs 27.21 grams per US fluid ounce — 8% lighter than water. These differences matter in baking, where precision affects texture and rise.

How to Calculate the Gram Weight of Any Fluid Ounce

To calculate the gram weight of 1 fluid ounce for any liquid, multiply the liquid's density (in g/mL) by the volume of 1 fluid ounce in milliliters (mL).

Use 28.4131 mL instead of 29.5735 mL for UK (Imperial) fluid ounces. The US fluid ounce is 4.1% larger than the UK fluid ounce.

Step-by-Step Example: Whole Milk

1. Find the density of whole milk: 1.03 g/mL
2. Multiply density by 29.5735 mL: 1.03 × 29.5735 = 30.46 g

1 US fluid ounce of whole milk weighs 30.46 grams.

Step-by-Step Example: Honey

1. Find the density of honey: 1.42 g/mL
2. Multiply density by 29.5735 mL: 1.42 × 29.5735 = 42.01 g

1 US fluid ounce of honey weighs 42.01 grams.

US Fluid Ounce vs UK Fluid Ounce: Weight Difference

The US fluid ounce and the UK (Imperial) fluid ounce have different volumes, which means the gram weight per fluid ounce differs between the 2 systems.

The US fluid ounce holds 1.1604 mL more liquid than the UK fluid ounce. Verify which system your recipe uses before measuring, especially when scaling international recipes.

Multi-Fluid-Ounce Weight Reference Table

The following table shows the gram weight for multiple fluid ounce quantities of water (density = 1.0 g/mL).

8 fl oz (1 cup) of water weighs 236.59 grams (0.237 kg or 0.522 pounds). 128 fl oz (1 gallon) of water weighs 3,785.41 grams (3.785 kg or 8.345 pounds).

3 Factors That Affect Fluid Ounce Weight

There are 3 factors that change the gram weight of a fluid ounce:

1. Density of the liquid — Denser liquids weigh more per fluid ounce. Honey (1.42 g/mL) weighs 54% more than vegetable oil (0.92 g/mL) for the same volume.
2. Temperature — Liquids expand when heated and contract when cooled. Water at 20 °C (68 °F) has a density of 0.9982 g/mL, while water at 4 °C (39.2 °F) has a density of exactly 1.0 g/mL. This 0.18% difference matters in laboratory settings but not in everyday cooking.
3. Measurement system (US vs UK) — A US fl oz holds 29.5735 mL, while a UK fl oz holds 28.4131 mL. Using the wrong system creates a 4.1% error in weight calculations.

Frequently Asked Questions

How much does 1 fluid ounce of water weigh in grams?

1 US fluid ounce (fl oz) of water weighs 29.5735 grams (g). 1 UK (Imperial) fluid ounce of water weighs 28.4131 grams. Water is the standard reference liquid because water has a density of 1.0 g/mL at 4 °C (39.2 °F).

Does every liquid weigh the same per fluid ounce?

No, the weight per fluid ounce varies by liquid density. 1 fl oz of honey weighs about 42.01 grams, 1 fl oz of whole milk weighs about 30.46 grams, and 1 fl oz of vegetable oil weighs about 27.21 grams. Use the formula Weight (g) = Density (g/mL) × 29.5735 to calculate the weight of 1 fl oz for any liquid.

How do I calculate the weight of a fluid ounce for any liquid?

Multiply the liquid's density (in g/mL) by 29.5735 mL (the volume of 1 US fluid ounce). For UK fluid ounces, multiply the density by 28.4131 mL. The density values for common liquids are: water (1.0 g/mL), whole milk (1.03 g/mL), vegetable oil (0.92 g/mL), olive oil (0.91 g/mL), honey (1.42 g/mL), and maple syrup (1.37 g/mL).