Balloon Arch Instructions: Calculate Arch Length & Number of Balloons

The first thing you need from our balloon arch instructions is the formula for calculating the required length of line, as this determines the number of balloons you'll need for your arch.

To figure out the size of the balloon arch you want to build, you need to measure the height and width of the area where it will be displayed. Use the following calculations to work out the approximate length of your arch line.

Fig. 1
To make an arch that's wider than it is tall:
width + height = approximate total length.

Fig. 2
For an arch that has the same height and width:
(1.5 x height) + width = approximate total length.

Fig. 3
For an arch that's taller than it is wide:
(2 x height) + width = approximate total length. 

How to calculate balloon arch length

Next, you need to calculate how many balloons you need. This depends on the type of balloon arch you have in mind and the size of the balloons.

Balloon Arch Instructions for a String of Pearls Arch

For a 'String of Pearls' arch (i.e a floating arch with a single row of balloons) you'll need about three 11" balloons per meter.

Example: Let's say your arch is 6m (20') wide and 6.7m (22') high. As your arch is taller than wide, formula 3 from above applies to calculate the arch length:

(2 x 6.7m) + 6.0m = 13.4m + 6.0m = 19.4 m

So your arch is roughly 20m long, which means you need 60 x 11" balloons (20m x 3 balloons per meter).

Balloon Arch Instructions for a Clustered Arch

If the length of the balloon arch and the diameter of balloons are in the same units (both in ft, in, m, cm, mm ) divide the diameter of the balloon into the length of the arch and multiple by 4.8 to get the number of balloons needed for an arch with clusters of 4 balloons (thanks to Sean O'Kelly from who shared this formula with our readers).

Length of arch (unit) 
--------------------------------                        x     4.8 = # of balloons 
Diameter of balloon (same unit) 

Example: You want to make an arch that is 6.1m (20') wide and 3.7m (12') high. You plan to use 11" balloons (28cm diameter). As your arch is wider than tall, formula 1 from above applies. We'll calculate everything in cm to stay with the same unit.

Arch length: 610cm + 370cm = 980cm 

Number of balloons: 980cm / 27cm * 4.8 = 174.2 balloons 

Number of 4-balloon clusters: 174.2 / 4 = 43.6

You have the choice of packing the arch a bit tighter with 44 clusters (176 balloons), or a bit less tight with 43 clusters (172 balloons). 

If you calculate everything in feet and inches, here's an easier way to estimate the number of balloons you need for a 4 balloon per cluster arch...

  • 5 inch balloons = 12 per foot 
  • 9 inch balloons = 8 per foot 
  • 11 inch balloons = 6 per foot 
  • 14 inch balloons = 4 per foot 
  • 16 inch balloons = 4 per foot 

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