Purpose Informal caregivers of individuals with cancer may experience substantial burdens. To develop interventions to support these caregivers, it is crucial to quantify and understand the domains of burdens potentially experienced by caregivers and factors contributing to each domain. Methods Using data from two national surveys, the National Survey of Caregiving (NSOC) linked to the National Health and Aging Trends Survey (NHATS), we identified all participants in the NHATS diagnosed with cancer who had a caregiver participating in the NSOC. Guided by a theoretical model, twenty-two items in the NSOC related to caregiver health, mood and outlook were included in factor analysis to develop scales capturing domains of burden. Multivariable regression analyses examined whether activities performed by caregivers and supports for caregivers were associated with these burden scales. Results Analysis of responses from 373 caregivers of cancer patients identified three scales: emotional burden; psychological burden; and relationship with the patient. Providing assistance managing medical care was associated with increased emotional and psychological burden, while assistance with non-medical issues increased psychological burden and worsened relationships with patients. Caregiver provision of direct patient care activities was also associated with increased burden but improved relationships with patients. Use of caregiver supports showed mixed associations with burden. Conclusions Using a nationally-representative sample of cancer patients and their caregivers and brief publicly-available survey questions, we present three scales addressing different aspects of caregiver burden that are responsive to caregiver activities and social supports. This may assist in developing and evaluating intervention to decrease caregiver burden.