Convert fluid volumes for intake and output (I&O) charting between US fluid ounces and millilitres. One fluid ounce is 29.5735 mL; many charts round to 30 mL per ounce.
| Common volume | fl oz | mL |
|---|---|---|
| Teaspoon | — | 5 |
| Tablespoon | 0.5 | 15 |
| Medicine cup | 1 | 30 |
| Small juice glass | 4 | 120 |
| Cup / mug | 8 | 240 |
| Soup bowl | 12 | 360 |
| Water pitcher | 32 | 950 |
I&O totals are only as accurate as the measurements behind them: measure with a graduated container where possible rather than estimating, and record in the unit your chart uses. Reference volumes in the table are the standard chart values used on most wards.
How many mL are in a fluid ounce?
One US fluid ounce is exactly 29.5735 mL. For bedside charting, most hospitals round to 30 mL per ounce, which is why a standard 8 oz cup is charted as 240 mL even though the exact conversion is about 237 mL.
What counts as intake and output?
Intake includes everything liquid that goes in: drinks, soups and liquid foods, ice (counted at roughly half its frozen volume on many charts), IV fluids and liquid medications. Output includes urine, vomit, liquid stool, drainage and wound losses that can be measured. Both are totalled per shift and per 24 hours.
Why do nurses chart I&O so precisely?
Fluid balance is an early signal of problems such as dehydration, kidney strain or fluid overload. Accurate I&O — measured, not eyeballed — lets the team spot a trend across shifts before it becomes an emergency.