Skip to main content
Calcimator

Firestop Joint Calculator

Calculate sealant volume, width-to-depth ratio, and backer rod sizing for fire-rated joint systems.

Inputs

%

Results

Width-to-depth ratio

2

Total sealant (fl oz)66.5
Cartridges needed7
Backer rod diameter (in)1.25
Min sealant class12
Material cost ($)$87.00
How to Use This Calculator
  1. Enter Joint width (in), Joint depth (in), and Joint length (ft).
  2. Set Fire rating (hrs) and Expected movement (%).
  3. Review the Width-to-depth ratio result.
  4. Use Total sealant (fl oz) and Cartridges needed to inform your decision.

How the result changes with Joint width (in)

Joint width (in)Width-to-depth ratio
0.711.43
2.184.36
3.947.88
5.4110.82

What each input means

Joint width (in)
Width of the joint opening.
Joint depth (in)
Depth of sealant in the joint.
Joint length (ft)
Total linear feet of joint to seal.
Fire rating (hrs)
Required hourly fire resistance rating.
Expected movement (%)
Expected joint movement as percentage of width.

What each result means

Width-to-depth ratio
Ideal ratio is 2:1 for optimal sealant performance.
Total sealant (fl oz)
Total firestop sealant volume needed.
Cartridges needed
Standard 10.1 oz cartridges required.
Backer rod diameter (in)
Recommended backer rod size (25% larger than width).
Min sealant class
ASTM C920 sealant movement class required.
Material cost ($)
Estimated sealant and backer rod cost.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Joint width (in) = 1, Joint depth (in) = 0.5, Joint length (ft) = 20, Fire rating (hrs) = 2 = 5 input(s) provided
  2. Calculate Width-to-depth ratio
    2 = 2
  3. Calculate Total sealant
    Total sealant
    66.5 = 66.5
  4. Calculate Cartridges needed
    Cartridges needed
    7 = 7

Engine last updated .

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Fire Stopping

Expansion Joint Gap Calculator

Calculate sealant volume, packing depth, and system type for expansion joint firestop based on gap width and movement.

Fire Stopping

Firestop Penetration Calculator

Calculate annular space, sealant volume, and packing depth for through-penetration firestop systems.

Fire Stopping

Head-of-Wall Joint Calculator

Calculate mineral wool, sealant, and deflection requirements for head-of-wall firestop joints.

Waterproofing

Joint Sealant Calculator

Sealant volume from joint width, depth, and linear footage.

Fire Protection

Fire Door Rating Calculator

Required fire rating from wall construction and occupancy.

More in Construction & Building Trades.