Mug Capacity Calculator
"How many ounces?" is the question every mug buyer asks. Measure the interior diameter and depth, allow a little headspace, and get the usable volume in ounces and milliliters — plus what it holds filled to the brim.
The gap you would leave when pouring — about half an inch is typical. Set to 0 for brim-full.
Formula & how it works
Volume is π × (diameter ÷ 2)² × fill depth, where fill depth is interior depth minus headspace. Cubic inches convert with × 16.387 for milliliters; centimeters give milliliters directly. Fluid ounces are mL ÷ 29.57.
Worked example
A mug with a 3.25 inch interior diameter and 4 inch depth, poured to leave half an inch of headspace, fills 3.5 inches deep. That is about 29 cubic inches — roughly 476 mL or 16.1 fl oz. Brim-full it would hold about 18.4 oz, which is why quoting the usable figure matters.
Sizing mugs people want
Quote what it pours
Brim-full capacity flatters a mug but nobody drinks that way. Leaving realistic headspace and quoting the usable number sets accurate expectations, and it is the figure a customer will check against their coffee maker or their favourite 12-ounce pour.
Diameter dominates
Volume scales with the square of the radius, so widening a mug adds capacity much faster than making it taller. A quarter inch more interior diameter changes the ounces noticeably — useful when a form is close to a target size and you would rather not alter the proportions.
Plan capacity before you throw
Since clay shrinks in every direction, volume drops roughly with the cube of the linear shrinkage: a 12% linear shrink takes away close to 30% of the interior volume. Work out the fired capacity you want, then size the wet form accordingly rather than discovering the shortfall after firing.