  The present study is the first of a series of three papers where we
characterise the type II supernovae (SNe~II) from the Carnegie Supernova
Project-I to understand their diversity in terms of progenitor and explosion
properties. In this first paper, we present bolometric light curves of 74
SNe~II. We outline our methodology to calculate the bolometric luminosity,
which consists of the integration of the observed fluxes in numerous
photometric bands ($uBgVriYJH$) and black-body (BB) extrapolations to account
for the unobserved flux at shorter and longer wavelengths. BB fits were
performed using all available broadband data except when line blanketing
effects appeared. Photometric bands bluer than $r$ that are affected by line
blanketing were removed from the fit, which makes near-infrared (NIR)
observations highly important to estimate reliable BB extrapolations to the
infrared. BB fits without NIR data produce notably different bolometric light
curves, and therefore different estimates of SN~II progenitor and explosion
properties when data are modelled. We present two methods to address the
absence of NIR observations: (a) colour-colour relationships from which NIR
magnitudes can be estimated using optical colours, and (b) new prescriptions
for bolometric corrections as a function of observed SN~II colours. Using our
74 SN~II bolometric light curves, we provide a full characterisation of their
properties based on several observed parameters. We measured magnitudes at
different epochs, as well as durations and decline rates of different phases of
the evolution. An analysis of the light-curve parameter distributions was
performed, finding a wide range and a continuous sequence of observed
parameters which is consistent with previous analyses using optical light
curves.
