The rare Hebrew verb kasas (כָּסַס) means to calculate, count, or estimate — specifically used in the context of reckoning how many people can eat from a Passover lamb. It appears only in Exodus 12:4, where Moses instructs that if a household is too small for an entire lamb, they should "estimate" (kasas) how many people are needed to consume it fully. The word emphasizes careful, deliberate calculation in worship.
Though kasas appears only once, its theological context is profound. The Passover regulations require that nothing be wasted and nothing be insufficient — the lamb must be fully consumed. This careful reckoning points to the sufficiency and completeness of the sacrifice. No portion of the Passover lamb was to be left over (Exodus 12:10), just as Christ's sacrifice on the cross is complete — "It is finished" (John 19:30). The act of calculating who can participate in the Passover also foreshadows the New Testament question of who may partake of Communion (1 Corinthians 11:28). Holy things require careful, deliberate preparation.