Bolometric corrections are used in quasar studies to quantify total energy output based on a measurement of a monochromatic luminosity. First, we enumerate and discuss the practical difficulties of determining such corrections, then we present bolometric luminosities between 1 μm and 8 keV rest frame and corrections derived from the detailed spectral energy distributions of 63 bright quasars of low to moderate redshift (z= 0.03–1.4). Exploring several mathematical fittings, we provide practical bolometric corrections of the forms Liso=ζ λLλ and log (Liso) =A+Blog (λLλ) for λ= 1450, 3000 and 5100 Å, where Liso is the bolometric luminosity calculated under the assumption of isotropy. The significant scatter in the 5100 Å bolometric correction can be reduced by adding a first-order correction using the optical slope, αλ, opt. We recommend an adjustment to the bolometric correction to account for viewing angle and the anisotropic emission expected from accretion discs. For optical/UV monochromatic luminosities, radio-loud and radio-quiet bolometric corrections are consistent within 95 per cent confidence intervals, so we do not make separate radio-loud and radio-quiet corrections. In addition, we provide several bolometric corrections to the 2–10 keV X-ray luminosity, which are shown to have very large scatter. Separate radio-loud and radio-quiet corrections are warranted by the X-ray data.