How much caulk do you need?

How many feet does a tube of caulk cover?

Divide the tube's volume by the volume of the bead per foot. A standard 10.1 fl oz cartridge holds 18.2 cubic inches. A ¼ × ¼ inch joint takes 0.25 × 0.25 × 12 = 0.75 cubic inch per foot, so one cartridge fills about 24 feet.

How many tubes of caulk do I need?

Measure the total length of the joints and divide by the feet per tube, then round up. 100 feet of ¼ × ¼ inch joint at 24.3 feet per cartridge is 4.1, so buy 5 cartridges.

How much does a corner bead take?

A bead run into an inside corner — along a tub or countertop — is roughly a triangle, half of a square joint. A ¼ inch corner bead takes 0.375 cubic inch per foot, so a 10.1 oz cartridge runs about 48 feet.

How deep should a caulk joint be?

Caulk and sealant makers usually ask for a joint about half as deep as it is wide on wider joints, with backer rod behind it — check the product label. Deep joints use far more caulk: a ⅜ × ⅜ inch joint takes 2.25 times as much as a ¼ × ¼ joint.

What sizes does caulk come in?

Standard cartridges for a caulk gun hold 10.1 fluid ounces; large "quart" cartridges hold 28 oz; squeeze tubes are often 5.5 oz. In metric, cartridges are usually about 300 ml.

How many cubic inches are in a cartridge of caulk?

A 10.1 fluid ounce cartridge holds 10.1 × 231 ÷ 128 = 18.2 cubic inches, because a US fluid ounce is 231 ÷ 128 cubic inches. A 300 milliliter cartridge holds about 18.3 cubic inches.

Why does the amount of caulk I use differ from the calculator?

The calculator assumes a joint that is filled completely and a bead of constant size. Uneven gaps, a bead that is bigger than the joint, a cut nozzle that is too wide and caulk left in the tube all change the real coverage. Treat the result as a minimum and buy one cartridge extra for a big job.

Is a wider joint or a deeper joint the bigger factor?

They count equally, because the volume per foot is width times depth. A joint that is twice as wide and twice as deep takes four times as much caulk.

How the calculation works

The amount of caulk per foot is the cross-section of the joint times 12 inches. A rectangular joint has an area of width times depth. A corner bead is treated as a right triangle with both legs equal to the bead size, so its area is half of the width squared. The cartridge volume in cubic inches is the fluid ounces times 231 ÷ 128. Dividing the cartridge volume by the volume per foot gives the feet one cartridge fills, and dividing the total joint length by that, rounded up, gives the number of cartridges.

Worked example

Suppose the total length of joints is 160 ft. For a ¼ × ¼ inch joint, one 10.1 oz cartridge covers 24.3 ft, so you need 7 cartridges. If the joint is ⅜ inch wide and ¼ inch deep, one cartridge covers only 16.2 ft and you need 10. A ¼ inch corner bead covers 48.6 ft per cartridge and takes 4. With 28 oz cartridges for the ¼ × ¼ joint, one covers 67.4 ft and the job takes 3.

Common mistakes

• Measuring the gap at its narrowest point. Gaps are rarely uniform. Use an average or the widest typical width so the estimate is not too low.
• Filling a deep gap with caulk alone. A deep joint wastes a lot of caulk. A backer rod behind the sealant limits the depth, and the product label gives the recommended depth.
• Counting tubes of different sizes alike. A 28 oz cartridge holds nearly three times as much as a 10.1 oz one, which can make it cheaper per foot even if the price looks higher.

Sources and related calculators

Volumes: the US gallon is defined as 231 cubic inches (NIST Handbook 44, Appendix C), which gives the cubic inches per fluid ounce; cartridge sizes are as stated on the product labels. Related: baseboard calculator, paint calculator and wallpaper calculator.