The one equation behind every feeding pump
Every continuous feeding calculation is the same division: rate equals volume divided by time. A prescription that reads 1000 mL over 20 hours becomes 1000 divided by 20, which is 50 mL per hour, and that is the number set on the pump. Run the division the other way and a rate of 50 mL per hour over 24 hours delivers 1200 mL in the day. Nothing more complicated is involved, and yet this small conversion sits between almost every enteral prescription and the pump that carries it out, because prescriptions are written in volumes per day and pumps accept only a rate per hour. The first mode of this calculator performs the conversion in the prescribing direction, volume and hours to rate. The second mode runs it backwards, rate and running time to delivered volume, which is the check used when a pump has been running and the team wants to know how much feed the patient has actually received, or when a rate is being considered and its daily total needs to be seen before it is prescribed. The chart at the top of the page shows the same relationship for two common daily volumes: the fewer the hours, the higher the rate must climb to deliver the same volume.
| Hours of feeding | Rate for 1000 mL | Rate for 1500 mL |
|---|---|---|
| 24 hours | 41.7 mL per hour | 62.5 mL per hour |
| 20 hours | 50 mL per hour | 75 mL per hour |
| 18 hours | 55.6 mL per hour | 83.3 mL per hour |
| 16 hours | 62.5 mL per hour | 93.8 mL per hour |
| 12 hours | 83.3 mL per hour | 125 mL per hour |
| 8 hours | 125 mL per hour | 187.5 mL per hour |
Pumps are set in whole millilitres per hour, so a computed rate of 83.3 is set as 83 or 84, delivering a little under or a little over the nominal volume across the full period. That rounding is inherent to the equipment and is absorbed within the prescribed plan; it is one reason feeding prescriptions are reviewed as daily totals and not only as the rate on the pump screen.
Cyclic feeding: the same volume in fewer hours
Continuous feeding over a full 24 hours is common in intensive care, but it is not the only pattern, and for many patients it is not the best one. Cyclic feeding delivers the day's prescribed volume over part of the day, frequently overnight, so that the patient is free of the pump for waking hours, therapy, mobilisation, and ordinary life. The nutritional content of the day is unchanged; only the delivery window shrinks, and the rate rises in exact proportion. A daily volume of 1200 mL is 50 mL per hour across 24 hours, 75 mL per hour across 16 hours, and 100 mL per hour across 12 hours. The trade off is tolerance: a higher rate asks more of the stomach and gut in each hour, so cyclic schedules are usually reached by progression from continuous feeding rather than started at full rate, and the window and rate are prescribed together. When a cyclic plan is being checked, the useful questions are the arithmetic ones this tool answers: does the rate multiplied by the window equal the prescribed daily volume, and does the higher rate stay within what the patient has been tolerating.
Bolus feeding: volume per feed times feeds per day
Bolus feeding replaces the pump's steady rate with discrete feeds, each given over a short period by syringe or gravity, more like meals. The arithmetic changes shape: the daily volume is the volume per feed multiplied by the number of feeds, so five feeds of 240 mL give 1200 mL in the day. Spacing follows from the count: feeds divided evenly across the day sit 24 divided by the number of feeds apart, so five feeds sit about 4.8 hours apart on paper. Real bolus schedules are usually arranged across waking hours rather than evenly around the clock, with the gaps shaped by sleep, medicines, and other care, and the care team sets the actual times. The even spacing this calculator reports is a reference figure for comparing with the prescribed schedule, not a timetable to follow. Bolus feeding is generally used where the feed enters the stomach and the patient tolerates discrete volumes; feeds delivered beyond the stomach, into the jejunum, are given continuously by pump because the small bowel does not hold a bolus the way the stomach does. Which pattern a patient has is a clinical decision; the calculator's third mode simply builds the totals for the bolus pattern once it has been chosen.
Free water flushes are part of the day's fluid
A feeding tube is flushed with water before and after feeds and medicines, and at intervals during continuous feeding. Flushing keeps the tube patent, clears feed and medication residue from the line, and forms part of the guidance in the ASPEN safe practices for enteral nutrition therapy, which call for regular water flushes as a routine element of tube care. The water in those flushes is not incidental: it enters the patient and belongs in the day's fluid accounting exactly as feed does. Six flushes of 30 mL deliver 180 mL of water, a quantity that matters for a patient on a fluid restriction, for a patient whose sodium is being watched, and for anyone whose intake is being balanced against output. Flush volumes and frequency are set by the care team for the individual patient, taking account of the tube, the medicines being given, and the patient's fluid allowance, and this calculator takes whatever amounts the user enters and adds them to the feed volume to produce the combined daily total. That combined figure, feed plus flush water, is the number that should appear in the day's intake record.
Starting, advancing, and the patients who need a slower start
Feeding rates are rarely started at the full prescribed rate. Standard practice is to begin at a lower rate and advance in steps as tolerance is shown, watching for vomiting, abdominal distension, pain, diarrhoea, and high gastric residuals where those are measured. The arithmetic of advancement is the same conversion again: each step is a rate, each rate delivers a known volume over the hours it runs, and the day's total during advancement is deliberately less than the target total. One group needs particular care. A person who has eaten little or nothing for an extended period can develop refeeding problems when nutrition restarts, as feeding drives shifts in phosphate, potassium, and magnesium; the ASPEN consensus recommendations on refeeding syndrome describe cautious initiation and close electrolyte monitoring in patients at risk. In such patients the starting rate, the advancement steps, and the monitoring are prescribed explicitly, and the calculator's role is confined to checking the volumes those steps deliver. Tolerance problems at any stage are a reason to contact the treating team, not to adjust the plan independently.
Checking the pump against the prescription
Because a single number on a pump delivers the whole prescription, a wrong rate delivers a wrong day of feeding, in either direction. A rate set too low underfeeds: across 24 hours, running at 40 mL per hour instead of 50 delivers 960 mL instead of 1200 mL, a shortfall that accumulates day after day in a patient who may already be malnourished. A rate set too high overfeeds and can outpace what the gut tolerates, and it also delivers fluid faster than intended, which matters in patients with heart failure or kidney impairment whose total fluid is restricted. The routine defences are arithmetic habits: read the rate back against the prescription, multiply rate by hours to confirm the daily volume, include flush water in the intake total, and recheck whenever the plan, the formula, or the pump changes. The second mode of this calculator is built for exactly that check, converting the rate as set into the volume it will deliver over the hours it will run.
Volume is not nutrition: the formula completes the picture
This calculator works in millilitres, and millilitres are only half of a feeding plan. What the patient actually receives nutritionally depends on the formula in the bag: its energy density in kilocalories per millilitre, its protein content, and its water content are all printed on the product label and differ between standard, high energy, high protein, and disease specific products. A day of 1200 mL of a 1.0 kcal per mL formula is a different prescription from 1200 mL of a 1.5 kcal per mL formula, even though the pump arithmetic is identical. Selecting the formula, setting the target volume, and deciding the rate and schedule belong to the prescribing team, usually with dietetic input, based on the patient's measured or estimated requirements and clinical state. This page deliberately stops at the volume arithmetic, and its results should always be read alongside the specific formula and the written prescription.
Sources
- Boullata JI, Carrera AL, Harvey L, et al. ASPEN Safe Practices for Enteral Nutrition Therapy. Journal of Parenteral and Enteral Nutrition. 2017;41(1):15-103. Routine water flushing of feeding tubes, verification of prescriptions, and safe delivery practice.
- da Silva JSV, Seres DS, Sabino K, et al. ASPEN Consensus Recommendations for Refeeding Syndrome. Nutrition in Clinical Practice. 2020;35(2):178-195. Cautious initiation of feeding and electrolyte monitoring in patients at risk of refeeding syndrome.
- Singer P, Blaser AR, Berger MM, et al. ESPEN guideline on clinical nutrition in the intensive care unit. Clinical Nutrition. 2019;38(1):48-79. Enteral feeding practice, progression, and tolerance monitoring in critically ill patients.
Key takeaways
- Divide the volume in millilitres by the number of hours over which it is to be given.
- 1500 divided by 18 is 83.3 mL per hour.
- Yes.
- Dividing the day evenly gives a first estimate: five feeds a day sit 24 divided by 5, or about 4.8 hours, apart.
Frequently asked questions
How do I convert a prescribed daily volume into a feeding pump rate?
Divide the volume in millilitres by the number of hours over which it is to be given. A prescription of 1500 mL over 20 hours gives 1500 divided by 20, which is 75 mL per hour. The same division works for any volume and any number of hours, and this calculator performs it in the first mode.
What pump rate delivers 1500 mL over 18 hours?
1500 divided by 18 is 83.3 mL per hour. Pumps are usually set in whole millilitres per hour, so a rate of 83 mL per hour delivers about 1494 mL in 18 hours and 84 mL per hour delivers about 1512 mL. Small rounding differences of this kind are a normal part of setting a pump and are handled within the prescribed plan.
Does flush water count toward the daily fluid total?
Yes. Water used to flush a feeding tube is fluid the patient receives, and it is recorded as part of the day's intake. Six flushes of 30 mL add 180 mL to the day, which is a meaningful amount for a patient whose fluids are being carefully balanced. This calculator adds flush water to the feed volume and reports the combined total.
How far apart should bolus feeds be?
Dividing the day evenly gives a first estimate: five feeds a day sit 24 divided by 5, or about 4.8 hours, apart. In practice bolus feeds are usually given across waking hours rather than evenly around the clock, and the actual times are set by the care team to suit the patient, other care, and medicines. The calculator reports the even spacing so the schedule can be compared with the prescribed one.
What is cyclic feeding?
Cyclic feeding means giving the day's feed volume over part of the day rather than continuously over 24 hours, commonly overnight for 8 to 16 hours so the daytime is free of the pump. The total volume is unchanged; the rate is higher because the same volume is delivered in fewer hours. A daily volume of 1200 mL runs at 50 mL per hour over 24 hours, at 75 mL per hour over 16 hours, and at 100 mL per hour over 12 hours.
Who decides the feeding rate and volume for a patient?
The prescribing clinical team, usually with a dietitian, decides the formula, the volume, the rate, and how the rate is increased, based on the patient's condition, gut function, fluid status, and nutritional requirements. This calculator only does the arithmetic inside a plan that has already been prescribed. It does not choose a rate for any patient, and a calculated rate should never replace or override a prescribed one.