How to measure joints for caulking

Measure each joint, its width and its sealant depth, then work out the sealant volume and the cartridges to order. A worked example and a free calculator are at the end.

Caulk calculator

What to bring

A tape measure or a laser measure for the lengths
A ruler or a joint gauge for the width and the depth
Something to note each joint: paper, or a MesuPro sheet on your phone

Safety first: at height, use the right access (lift, scaffold or swing stage) with its fall protection, and never work alone. Note the access each joint needs in the survey: it matters for the estimate too.

Step by step

Go elevation by elevation
Note each joint on its own line: window and door perimeters, vertical and horizontal facade joints, control and expansion joints. Joints of the same size can share a line with their total length.
Measure the length
Along the joint, in feet (or meters). For an opening, it is its perimeter.
Measure the width and the depth
The width of the joint and the depth the sealant will fill, in inches (or millimeters). Measure at several points: joints are rarely even. For the right depth for a given width, follow the sealant maker's guidance.
Work out the cartridges
Volume = length x width x depth, added up for all the joints. In feet, the volume is in gallons and the cartridges are 10.1 oz; in meters, the volume is in liters and the cartridges are 300 mL. Both add 10% waste and round up to the next cartridge.

The calculation

In feet, as in the feet survey template: volume = length x 12 x width x depth / 231 gallons, cartridges = volume x 128 x 1.1 / 10.1 (10.1 oz cartridges, 10% waste). In meters, as in the metric template: volume = length x width x depth / 1000 liters (width and depth in mm), cartridges = volume x 1.1 / 0.3 (300 mL cartridges). Rounded up to the next cartridge.

Worked example

Two joints: 120 ft at 0.5 in wide and 0.25 in deep, and 40 ft at 0.75 in wide and 0.375 in deep: 1.36 gallons of sealant, so 20 cartridges of 10.1 oz with 10% waste.

Try it with your numbers

Common mistakes

Measuring the joint opening instead of the sealant depth: a backer rod changes the depth to fill.
Measuring the width at one point only.
Forgetting the joints around openings: windows and doors add up quickly.
Counting with another cartridge size than the one you will buy: the calculator counts 10.1 oz or 300 mL cartridges.