This versatile HVAC calculator helps size supply and return duct systems using the equal friction or velocity reduction method. Its dual-sided design features duct sizing scales and air properties on the front, and fitting equivalents, pressure drop charts, and essential HVAC formulas on the back. Built from durable, water-resistant paper with glued edges and riveted corners for long-lasting use. A practical reference tool that includes recommended duct velocities, sheet metal gauges, and more. Compact at 4" x 8.5", it fits easily in tool belts or bags.