01 · Overview
About this opioid conversion calculator
This calculator does one job: convert a single opioid dose or regimen line into its equivalent for another drug or route, with every step of the math visible. It normalizes the source drug to total daily morphine milligram equivalents (MME), divides by the target drug's factor, and applies whatever cross-tolerance reduction you choose — nothing is adjusted silently.
Single conversions are where dosing errors concentrate: a wrong factor, a per-dose number treated as a daily total, or a skipped cross-tolerance reduction can each produce a dangerous order. The visible calculation steps exist so you can verify each stage against your own reference before anything reaches the chart.
02 · Method
How the conversion math works
Every conversion runs the same three steps. First, the source dose is normalized to a total daily amount (if you enter a per-dose value with a frequency, the tool multiplies it out — a classic error source it makes explicit). Second, the daily dose is multiplied by the source drug's MME factor to get 24-hour morphine equivalents. Third, that MME total is divided by the target drug's factor, and any cross-tolerance reduction you selected is applied last.
Route matters: oral and IV forms of the same drug have different factors (IV morphine is roughly three times as potent as oral; IV hydromorphone roughly five times its oral form). The calculator uses route-specific factors wherever they exist and shows which factor it used in the steps.
03 · Exceptions
Special conversions that do not fit a simple multiplier
Methadone has no single conversion factor: its potency relative to morphine rises steeply with the pre-rotation dose (from roughly 4:1 at low doses to 12:1 or more at high doses), and its long, variable half-life causes delayed accumulation. Buprenorphine, a partial agonist with very high receptor affinity, is explicitly excluded from MME arithmetic by the CDC's 2022 guideline. This calculator refuses to output a number for either drug rather than pretend a multiplier exists — use a dedicated protocol with specialist input.
Transdermal fentanyl converts by ranges, not a point estimate (25 mcg/h ≈ 60–90 mg oral morphine equivalents per day), and is only for opioid-tolerant patients. Use the dedicated fentanyl method in the regimen builder, which rounds to real patch sizes and applies frail-patient reductions.
04 · Rotation
Cross-tolerance: the calculated dose is not the starting dose
Tolerance to one opioid transfers only partially to another. When switching agents in an opioid-tolerant patient, standard practice is to reduce the calculated equianalgesic dose by 25–50% and re-titrate with breakthrough doses available. The reduction field defaults to your explicit choice rather than applying one silently — select it deliberately based on pain control, frailty, organ function, and the agents involved.
05 · Built-in guardrails
Safety checks this tool applies
06 · Frequently asked questions
Frequently asked questions
How many mg of morphine equals 20 mg of oxycodone?
Oral oxycodone has an MME factor of 1.5, so 20 mg/day of oxycodone ≈ 30 mg/day of oral morphine. Remember that the equianalgesic result is a starting estimate: when actually rotating drugs, reduce it by 25–50% for incomplete cross-tolerance and titrate to effect.
What is the IV to PO ratio for morphine?
IV morphine is roughly three times as potent as oral morphine — 10 mg IV ≈ 30 mg PO. Hydromorphone's oral-to-IV difference is even larger (roughly 4 oral vs 20 IV as MME factors). This is why the calculator asks for the route on both sides of a conversion.
Should I reduce the dose when switching opioids?
Usually yes. Cross-tolerance between opioids is incomplete, so the standard approach is to reduce the calculated equianalgesic dose by 25–50% and provide breakthrough coverage while re-titrating. Frail, elderly, or opioid-sensitive patients warrant the larger reduction.
Why won't this calculator convert methadone or buprenorphine?
Because no single factor is safe. Methadone's ratio is nonlinear and dose-dependent, with delayed accumulation from its long half-life; buprenorphine is a partial agonist the CDC explicitly excludes from MME math. Both switches are protocols, not calculations — involve pain, palliative, or addiction medicine.
Is the result a recommended prescription?
No. It is an arithmetic starting estimate built from population-average factors. Age, organ function, drug interactions, pain trajectory, and tolerance all change the safe answer. Verify the math, apply clinical judgment, and reassess the patient soon after any switch.
Should I enter a per-dose amount or the daily total?
Either — but be explicit. Enter the total daily dose directly, or enter a per-dose amount and tick 'include frequency' so the tool multiplies it out visibly. Treating a per-dose number as a daily total (or vice versa) is one of the most common conversion errors.
07 · Sources
References
- Dowell D, Ragan KR, Jones CM, Baldwin GT, Chou R. CDC Clinical Practice Guideline for Prescribing Opioids for Pain — United States, 2022. MMWR Recomm Rep. 2022;71(3):1–95.
- CDC. Calculating total daily dose of opioids for safer dosage (MME conversion reference).
- Fine PG, Portenoy RK. Establishing 'best practices' for opioid rotation: conclusions of an expert panel. J Pain Symptom Manage. 2009;38(3):418–425.
- McPherson ML. Demystifying Opioid Conversion Calculations: A Guide for Effective Dosing. 2nd ed. ASHP; 2018.