Estimate balloons needed for a party.
A balloon garland is denser than people expect: a packed arch uses roughly four balloons per balloon-diameter of length, so smaller balloons need far more per metre, not fewer. Clusters are counted separately because only they normally need helium, and cylinder capacity scales with the cube of diameter — a 45 cm balloon holds about four times the helium of a 28 cm one.
Arch density
balloons per metre = (100 / balloon cm) x 4
Total
arch balloons + clusters x balloons per cluster
Helium
cylinder capacity scales as (28 / size)^3 from a 50-balloon baseline
Because density is set by diameter. Halving the diameter doubles how many fit along the same length, so a 13 cm filler garland uses roughly twice as many balloons per metre as 28 cm.
No. Garlands and arches are air-filled and held on a strip or frame, which is why only the cluster count drives the cylinder estimate.