Students measure, estimate, compare, add, and subtract lengths using rulers, number lines, and appropriate customary or metric units, including common halves and fourths, and find perimeters or missing side lengths in whole-number polygons. Students understand area as covering with square units, find it by counting arrays or multiplying the whole-number side lengths of rectangles, and measure, estimate, compare, and solve problems with mass in grams and kilograms and capacity in milliliters and liters, recognizing that 1 kilogram equals 1,000 grams and 1 liter equals 1,000 milliliters. Students read time to the nearest minute, use a.m. and p.m., determine elapsed time within and across hours, interpret calendars, and solve measurement problems involving addition, subtraction, multiplication, division, comparisons, and missing measures while preserving appropriate units.