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Not how many patients. How much care
Acuity-based staffing weights each patient by the amount of care they need, rather than counting heads. Instead of twenty-two patients, the unit has a weighted workload, and the nurses required are calculated from that. It is the number a flat ratio misses, because a flat ratio assumes every patient is the same shift.
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How do I calculate staffing by acuity?
Count the patients at each acuity level, give each level a weight, and the weighted total divided by your ratio, rounded up, is the staffing the unit needs. Enter the counts below.
Applied to the weighted workload, not to the headcount.
| Acuity level | Patients | Weight | Weighted |
|---|---|---|---|
| Level 1: self-caringMobile, independent, waiting on a letter. | 2 | ||
| Level 2: standardThe baseline the ratio assumes everyone is. | 10 | ||
| Level 3: heavyFrequent intervention, assistance to move. | 6 | ||
| Level 4: total careUnstable, or two people for every movement. | 4 | ||
| Total | 20 | patients | 22 |
Weighted workload is each level's patient count times its weight, added up. Required nurses is that total ÷ the ratio, rounded up. The weights are yours to argue about: the defaults are conventional, not a standard.
Required: by acuity
5
From a weighted workload of 22.
Required: flat ratio
4
From a headcount of 20, ignoring acuity.
A headcount ratio would call this unit staffed at 4. The work in the beds needs 5. That difference is the shift everybody remembers.
Computed in your browser. Nothing you type here is sent anywhere.
At a glance
- Acuity-based staffing weights each patient by care needed. A total-care patient might be counted as two, a self-caring patient as half, against a baseline of one.
- Required nurses come from the weighted workload rather than the raw census, then get rounded up, the same last step as a flat ratio.
- A headcount ratio and an acuity calculation agree exactly when every patient is average, which is a unit that does not exist.
- The gap between the two numbers is the point. A unit of twenty patients that is heavy can need more nurses than a unit of twenty-six that is light, and a ratio cannot see it.
- The weights are yours. This tool does the arithmetic; deciding what a level-four patient is worth is a clinical judgement it cannot make for you.
What is acuity-based staffing?
Acuity-based staffing decides how many nurses a unit needs from how much care its patients require, rather than from how many of them there are.
The mechanism is a weight. Each patient is scored, usually onto three to five levels, and each level carries a multiplier against a baseline of one. A patient who is total-care, unstable, or two-person for every movement counts as more than one; a patient who is dressed, mobile and waiting on a discharge letter counts as less. Add the weights instead of the heads and you have a workload rather than a census, and the staffing calculation runs off that.
The reason it exists is that the alternative is visibly wrong to everyone who has worked a shift. Every nurse can tell you about the night with fourteen patients that was worse than the night with twenty-two, and a headcount ratio has no way to express that; it is the same number on both nights, confidently. Acuity is an attempt to put the thing everybody already knows into a figure that a roster and a budget can read.
It is not a solved problem and this page is not going to pretend otherwise. The scoring is a judgement, judgements drift, and an acuity system where the levels are assigned by the person who wants more staff has a predictable failure mode, as does one where they are assigned by the person paying for them. The weights below default to something conventional and they are editable, because the arithmetic is the easy half and we cannot do the hard half for you.
How is acuity different from a nurse-to-patient ratio?
A ratio counts patients; acuity counts work. They give the same answer only when every patient on the unit happens to be exactly average, which is not a real unit.
Put the two side by side on a real evening and the difference stops being theoretical. Twenty patients at 1:5 requires four nurses, flatly, regardless of who those twenty are. If six of them are total-care and score at two, the weighted workload is twenty-six and the same 1:5 requires six: a fifty per cent difference in the staffing of the same unit, on the same evening, produced entirely by information the ratio was structurally incapable of holding. The calculator above shows both numbers together for exactly that reason: the gap is the argument.
Which is not to say the ratio is useless. A ratio is a floor, it is simple, it is enforceable, and where it is law it is law: California's Title 22 sets one licensed nurse to five patients on medical-surgical units, and no acuity argument in either direction changes that obligation. An acuity system that produces a number below the ratio you are held to has produced an interesting number and a compliance problem. Acuity properly sits on top of the floor rather than instead of it: the ratio says what you may not go below, and acuity says when the floor is nowhere near enough.
What this calculator cannot decide for you
The weights, which is the only genuinely difficult part of acuity-based staffing.
Whether a level-three patient is worth 1.5 nurses' attention or 1.75 is a clinical judgement about your patients on your unit, and it is the number the entire calculation turns on. Get the weights wrong and you have produced a precise figure that is confidently incorrect, which is worse than an obviously rough one. The defaults here are conventional rather than authoritative, and they are editable because they should be argued about by people who know the unit.
The other thing it cannot do is remember. Acuity is only worth measuring if last month's is still there to compare with; the value of the number is mostly in the trend, in showing that the unit has been running heavy for six weeks while the census looked flat. That needs the acuity captured next to the roster, every day, rather than typed into a page and lost when the tab closes. MedAligna carries an acuity multiplier on the census entry itself, so required staffing reflects it continuously and the same data feeds the reporting a survey asks for.
Questions people actually ask
- What is an acuity level?
- A score for how much nursing care a patient needs, usually on a three-to-five level scale, from self-caring up to total care. Each level carries a weight against a baseline of one, and the weights are what turn a count of patients into a measure of work.
- How do I calculate acuity-based staffing?
- Multiply the number of patients at each level by that level's weight, add them up to get a weighted workload, divide by your patients-per-nurse ratio, and round up. It is the ratio calculation with a better numerator.
- Does acuity replace the nurse-to-patient ratio?
- No, and it is important that it does not. Where a ratio is set in law (California's Title 22 sets 1:5 on medical-surgical units), it is a minimum you owe regardless of what an acuity model says. Acuity sits on top: the ratio is the floor, acuity is what tells you the floor is not enough tonight.
- What weights should I use?
- The ones your unit can defend. The defaults here are conventional starting points, not a standard, and they are editable for that reason. The weighting is a clinical judgement about your patients and it is the part of this that actually matters; the arithmetic is trivial and we have done it for you.
- Is my data sent anywhere?
- No. It computes in the browser and nothing leaves it. There is no account, and there is nothing to recover if you close the tab.
Sources
- California Code of Regulations, Title 22 — Licensed nurse-to-patient ratios – California Department of Public Health. Checked 2026-07-13.
Ratio and duty-hour requirements change, and they differ by state, by unit and by shift. These are the primary sources; your state board of nursing and your own employer's policy are what actually bind you.
Related
Acuity that is still there next month
MedAligna carries acuity on the census itself, so required staffing reflects it continuously and the trend is there when someone asks. Fourteen days free.