House battery capacity is measured in amp- hours. The amp-hour rating is unimportant for starting batteries; instead, what matters is how many cold-cranking amps (CCA) the battery can deliver at 0°F. Marine-cranking amps (MCA) is this same value measured at 32°F and will be higher. A marine diesel starting battery should have 2 to 3 amps per cubic inch of engine displacement (120 to 180 amps per liter).
Amp-hours are what counts for house batteries. Amp-hour requirements can be tabulated by
adding up the amperage of every electrical device multiplied by its hours of expected daily use. The house battery bank should be sized at three to four times this daily amp-hour budget. Another metric for sizing house batteries is the number of reserve minutes, which measures how long the battery can deliver 25 amps before falling to 10.5 volts, or dead flat, far below where you should ever let it drop. This reserve minutes rating is less important than the number of amp-hours.