Hydromorphone (Dilaudid) is stronger on a dose-basis, but you can calculate equivalent doses among other opioids. Other issues come into play as likely more important than "strength," e.g., route, active-metabolite production and clearance, as well as cost.
You could try this one to start with.
http://clincalc.com/Opioids/
There is variance out there among equianalgesic charts, depending on the data sets used.
Beware conversions to methadone!
Initial dosing is very complicated, due to opioid tolerance, opioid-opioid cross-tolerance, renal (pH-dependent urinary excretion) and hepatic function (chronic dosing induces its own CYP450 metabolism), and non-opioid, drug-drug interactions (many), and thus a very subject-dependent variation in 1/2-life. There is surprisingly little hard data on which to base this consequential decision. But, from the available data it is clear the methadone equianalgesia is very non-linear, which adds to the danger of overdosing a patient.
http://paindr.com/methadone-dose-conversion/
Analgesic effects of methadone are short-lived, so analgesic dosing is generally in divided doses TID-QID, whereas methadone maintenance dosing is once daily. Dosing changes should be very conservative, and because of the variable, but likely long 1/2-life (8-59 hours), be very, very patient, e.g., 10%-increases, closely monitored over 5-7 days for pharmacokinetic equilibration. Psychosocial functioning and support in patient-selection is key for these safety reasons.
The deaths of patients placed on methadone for analgesia are likely due to clinicians in busy practices, who are lacking training and experience with this useful, but tricky drug, prescribing it in cursory fashion.
So, kids don't try this at home! Get training, read about all the pitfalls, make time for appropriate and careful calculations, double-check yourself, shoot low (choose the conservatively low figure in the range), go very, very slowly. Only use methadone for chronic pain that is not going anywhere, so there's no rush to control the pain with methadone alone, depend on a range of dosing of short-acting opiates to control pain in the interim, as serum levels of methadone are glacially coasting up over a period of days. Continue to monitor them looking for metabolic changes in pharmacokinetics, for all the above reasons. Plus, there's likely going to be some QT/QTc-prolongation, so, baseline EKG, and at 6-months intervals thereafter.
If you cannot do all these things in managing methadone, then leave it to the professionals, and refer the patient to a subspecialist who manages chronic pain.
