Convert between milliliters, ounces, cups, liters, and more. Instant conversions with step-by-step explanations for cooking, travel, and daily use.
Formula:
Our converter uses milliliters (ml) as the base unit. All conversions first convert to ml, then to your target unit. This ensures accuracy and consistency across all measurements.
The metric system (ml, liters) is used worldwide and based on powers of 10. The US customary system (ounces, cups, gallons) has different conversion factors. This calculator handles both seamlessly.
This calculator uses US customary measurements. UK/Imperial measurements differ slightly (e.g., UK fluid ounce = 28.4131 ml). For cooking, these small differences usually don't matter, but be aware if precision is critical.
Convert recipe measurements between metric and imperial. Essential when using international recipes or adjusting serving sizes.
Know if your liquids meet the 3.4 oz (100 ml) TSA limit. Convert bottle sizes to ensure airport security compliance.
Convert cocktail recipes from ml to oz or vice versa. Understand jigger sizes and standard pours (1.5 oz = 44 ml).
Convert liquid medication doses accurately. Know that 1 teaspoon = 5 ml for proper dosing (though always follow your doctor's instructions).
Volume conversion looks easy until you start mixing systems. The biggest trap is assuming every "ounce," "cup," or "gallon" means the same thing. In reality, US customary, Imperial, and metric conventions can produce different values for the same word. For routine home cooking that difference may be small, but in lab prep, medication measurement, and manufacturing fill targets, it can be significant.
A reliable strategy is to pick one base unit and convert through it every time. This calculator uses milliliters as that base. The process is: convert from source unit to mL, then from mL to target unit. That two-step method prevents chain-rounding errors that happen when people convert cup to ounce to tablespoon to teaspoon repeatedly.
You can think of the math as:
value_ml = value_source × factor_source_to_ml
value_target = value_ml / factor_target_to_ml
Suppose you want to convert 2.5 US cups to liters. First convert cups to mL: 2.5 × 236.588 = 591.47 mL. Then divide by 1000 to get liters: 0.59147 L. If you instead round too early (for example, treating 1 cup as exactly 240 mL), the result becomes 0.600 L. That may be fine for a quick recipe but not for process control.
Another common issue is mass versus volume confusion. A milliliter is volume, while grams measure mass. They only match numerically for water near room temperature, where 1 mL is approximately 1 g. Oils, syrups, and powders have different densities, so 10 mL does not always equal 10 g. If your task involves density-sensitive materials, first convert volume accurately, then apply density separately.
Travel and regulatory contexts add one more wrinkle: labels and legal limits usually use metric values. TSA uses 100 mL for carry-on liquids, which is close to but not exactly 3.4 US fluid ounces. If your bottle label uses ounces only, converting to mL avoids uncertainty at screening. The same principle applies in healthcare, where doses are typically prescribed in mL and concentration (mg/mL) rather than kitchen spoons.
For best accuracy, keep at least 4-5 significant digits during intermediate calculations and round only the final value to a practical precision. Also record the unit explicitly every time. Writing just "15" without "mL" or "tbsp" is how preventable errors happen. A simple rule helps: number + unit, always together. If you follow that rule and convert through a stable base unit, your results stay consistent across cooking, science, logistics, and everyday measurement tasks.
Official measurement standards and conversion factors from the National Institute of Standards and Technology
Official U.S. travel guidance for 3.4 oz (100 ml) carry-on liquid limits
Official NIST reference for metric and imperial unit conversions