What would be the conversion dosage from hydromorphone to methadone?

for example if the what the methadone equivalent be of 16mg of hydromorphone
My mother has pancreatic cancer and they switched from hydromorphone to methadone orally. I'm not asking this to decide for her I was just wondering if she was taking the right equivalent dosage.

: http://alcoholdrugstreatment.info/what-would-be-the-conversion-dosage-from-hydromorphone-to-methadone