Caulk Calculator
Estimate how many tubes of caulk or sealant you need across any number of joints, with code-correct depth so you do not over-buy on wide gaps.
Uses the tube size you pick below. The result is the linear feet you can seal with that many tubes.
Standard fill covers cosmetic caulk. Sealant joint applies the ASTM C1193 depth cap and backer rod on joints wider than 1/2 in, which is where most calculators over-buy.
Rectangular fills the whole gap and is the safe default. Triangular is a corner fillet; concave is a tooled half-round bead.
The 10.1 oz cartridge fits a standard caulk gun. Sausages hold more but need a barrel gun.
Used only when Tube size is set to Custom. Open from a product label if it is not a standard size.
Your Caulk Estimate
- Add your joints - use a quick-add preset (window, tub, siding, expansion) or set the width, depth, and length for each joint, and add a row for every different joint on the job.
- Pick the joint type - standard fill for cosmetic caulk; sealant joint with backer rod for wide or moving joints, which applies the code depth cap.
- Set the bead shape - rectangular fill is the safe default; pick triangular or concave only if you tool that profile.
- Choose your tube size - the 10.1 oz cartridge is standard; larger sausages need a barrel gun.
- Buy the tube count shown - from one color lot, with a spare for tooling and future touch-ups.
How much caulk you need comes down to three things: joint width, joint depth, and total length. A standard 10.1 oz cartridge fills about 24 linear feet of a 1/4 in by 1/4 in joint filled flat, or roughly 30 feet if you tool a rounded bead. Add the length of every joint, pick your bead size, and the calculator rounds up to whole tubes. On joints wider than 1/2 in, switch to sealant mode: the code-correct depth is half the width with backer rod behind it, which cuts the caulk you buy roughly in half compared with filling the full gap.
What a Caulk Joint Looks Like
Caulk Coverage by Joint Size
These are linear feet a standard 10.1 oz cartridge fills, figured from the verified tube volume. The flat-fill column is the conservative case that matches manufacturer labels; a tooled concave bead of the same size stretches roughly 27% further. The rows for joints wider than 1/2 in already show the code depth, which is why a 3/4 in joint reads at 3/8 in deep:
| Joint (W x D) | Typical use | Flat fill | Concave bead |
|---|---|---|---|
| 1/8 x 1/8 | Fine trim, molding | 98 ft | 124 ft |
| 3/16 x 3/16 | Baseboard, casing | 43 ft | 55 ft |
| 1/4 x 1/4 | Windows, tub/shower, siding | 24 ft | 31 ft |
| 3/8 x 3/8 | Wider siding and trim gaps | 11 ft | 14 ft |
| 1/2 x 1/2 | Wide gap, filled full depth | 6 ft | 8 ft |
| 3/4 x 3/8 | Expansion joint at code depth | 5 ft | 7 ft |
| 1 x 1/2 | Wide expansion joint at code depth | 3 ft | 4 ft |
Figures use a 300 mL / 10.1 oz cartridge at 18.3 cubic inches, the nominal full volume. Real usable coverage runs slightly lower because some product stays in the nozzle and base, which the waste factor absorbs. As a sanity check, Liquid Nails LC-130 rates 30 ft per tube at a 1/4 in bead, matching the concave column.
Why Most Caulk Calculators Tell You to Buy Too Much
The common failure is a wrong tube volume or a wrong depth. One widely cited caulk calculator states that a standard tube holds 27 cubic inches and covers 432 feet at a 1/4 in by 1/4 in joint. A real 10.1 oz cartridge holds about 18.3 cubic inches, and 18.3 divided by a 1/16 square inch cross-section is roughly 24 feet, not 432. That page is off by about 18 times. Every number here traces back to the measured tube volume and the joint geometry, so the tube count is the amount the job actually takes.
The subtler over-buy happens on wide joints. Most calculators multiply the raw width by the raw depth, so a 1 in wide by 1 in deep expansion joint reads as a full square inch of cross-section per foot. On a real sealant joint that is wrong: the code-correct depth is half the width, capped at 1/2 in, with a backer rod filling the space below the bead. That halves the cross-section to 1/2 square inch per foot. Sealant mode applies this automatically, so a wide joint shows the amount you need with backer rod, not double it. The backer rod also does the real work of the joint, setting the depth and preventing the bead from bonding to three sides, which is what makes a joint tear early.
The Caulk Formula
Caulk volume is a cross-section times a length. W is the joint width, D is the bead depth, and the shape factor accounts for how the bead sits in the gap (all dimensions in inches):
Linear ft per tube = tube volume / cross-section / 12
Tubes (rounded up) = total length (ft) x 12 x cross-section / tube volume x (1 + waste)
Shape factors = rectangular fill 1.0, triangular bead 0.5, concave bead 0.785
ASTM C1193 depth = W up to 1/2 in: D = W. 1/2 to 1 in: D = half W (min 1/4 in). Over 1 in: D capped at 1/2 in.
The depth rule is the part competitors skip. On any joint wider than 1/2 in, filling the full gap over-buys caulk, because the sealant only occupies the top half of the depth and backer rod fills the rest.
Worked Examples
One window: a 3 by 5 ft window has about 16 feet of perimeter. At a 1/4 in by 1/4 in bead that is roughly two thirds of a tube, so one 10.1 oz cartridge does a standard window with room to spare. A whole house of 15 similar windows runs about 240 feet, or 11 tubes with 10% waste. That is why a single window almost always takes one tube and a full window job takes closer to a dozen.
Tub and shower surround: figure about 15 feet of joint around a standard tub and its wall corners. Tooled as a concave 1/4 in bead in mildew-resistant silicone, that is under one tube, so plan on one and keep a second for the inevitable re-tool. Silicone is correct here for the wet area, and it is not paintable, which is fine because the bead stays exposed.
Wide expansion joint: a 40 ft run of 3/4 in concrete control joint. Filled full depth the naive way, that reads as 17 tubes. Run in sealant mode, the depth caps at 3/8 in with backer rod behind it, and the job drops to 9 tubes. The backer rod costs a few dollars a roll and saves nearly half the caulk, and the joint performs better because the bead can stretch.
Which Caulk to Use
Match the caulk to the job before you match the amount. The wrong chemistry fails early no matter how much you buy:
| Type | Paintable | Best for | Standard |
|---|---|---|---|
| Silicone | No | Wet areas, glass, metal, high-movement joints | ASTM C920, Class 25-50 |
| Siliconized acrylic | Yes | Painted trim, baseboard, low-movement gaps | ASTM C834 |
| Polyurethane | Yes | Concrete, masonry, traffic and exterior joints | ASTM C920 |
| Butyl rubber | After it cures | Metal, gutters, roofing laps | Low movement |
Two rules save most callbacks. Use a mildew-resistant silicone or kitchen-and-bath sealant in tubs, showers, and around sinks. On concrete and masonry use a neutral-cure product, because acid-cure silicone attacks fresh cement, and prime porous substrates first. Where the bead has to be painted, such as interior trim, use a paintable acrylic or polyurethane, not straight silicone.
Sources & Standards
- Joint geometry follows ASTM C1193: a minimum 1/4 in by 1/4 in joint, depth equal to width up to 1/2 in, depth of half the width (minimum 1/4 in) from 1/2 to 1 in, and depth capped at 1/2 in above 1 in, with a backer rod sized about 25% larger than the joint to set the depth and prevent three-sided adhesion.ASTM C1193, Standard Guide for Use of Joint Sealants
- Sealant movement classes come from ASTM C920, which rates elastomeric sealants by class (Class 25 handles plus or minus 25% joint movement, Class 50 handles plus or minus 50%). Paintable latex and acrylic caulks are covered by ASTM C834 instead.ASTM C920, Standard Specification for Elastomeric Joint Sealants
- Coverage is computed from the verified cartridge volume: a 300 mL / 10.1 oz tube holds about 18.3 cubic inches (1 US fl oz = 1.8046875 cubic inches). The result was cross-checked against a manufacturer label, Liquid Nails LC-130 (ASTM C834), which states 30 linear feet per tube at a 1/4 in bead.
Around the Job
Caulking is usually the step before paint and part of finishing an exterior. The jobs next to it:
Related Calculators
Pair this with the rest of the surface tools. See the full surface calculator collection for tile, grout, paint, drywall, and more.
Frequently Asked Questions
How many tubes of caulk do I need?
It depends on the joint size and total length, not a fixed number per foot. A standard 10.1 oz tube fills about 24 feet of a 1/4 in by 1/4 in joint, so a job with 100 feet of that joint needs about 5 tubes with waste. Add every joint above and the calculator rounds up to whole tubes.
How many feet does a tube of caulk cover?
A standard 10.1 oz cartridge covers about 24 linear feet at a 1/4 in by 1/4 in joint filled flat, or roughly 30 feet if you tool a rounded bead. Smaller joints go much further: a 1/8 in bead reaches close to 100 feet, while a 1/2 in joint drops to about 6 feet per tube. Coverage scales with the width times the depth.
How many tubes of caulk do I need per window?
About one tube for a standard window. A 3 by 5 ft window has roughly 16 feet of perimeter, which is about two thirds of a 10.1 oz tube at a 1/4 in bead. Large or older windows with wider gaps can take a full tube or a little more, so buy one per window plus a spare.
How much caulk do I need for a shower or tub?
Plan on one to two tubes of mildew-resistant silicone for a standard tub and shower surround, which is roughly 15 feet of joint. Silicone is the right choice for the wet area and does not need painting. Buy two if the old caulk has to be cut out and redone, since re-tooling uses extra.
How much caulk do I need for baseboards?
A 12 by 12 ft room has about 48 feet of baseboard, which is roughly one tube at a 1/8 in bead. Use a paintable acrylic or siliconized-acrylic caulk on trim so it takes paint. Measure the total run of baseboard and enter it as one joint above for an exact count.
Do I need backer rod?
Yes for any joint deeper than 1/2 in or wider than 1/2 in. Backer rod is a foam cord pushed into the gap that sets the sealant depth, keeps the bead from bonding to three sides, and stops you from wasting caulk filling a deep gap. Size it about 25% larger than the joint width so it holds by friction. Switch on sealant mode above and the calculator applies the code depth for you.
Can I paint over caulk?
Not over pure silicone; paint beads off it. Use a paintable acrylic latex, siliconized acrylic, or polyurethane where a painted finish has to go over the bead, such as interior trim and baseboards. Silicone is best left where it stays exposed, like a tub or shower joint.
What is the right depth for a caulk joint?
For a sealant joint, depth equals width up to 1/2 in wide. From 1/2 to 1 in, depth is half the width with a 1/4 in minimum, and above 1 in the depth is capped at 1/2 in, with backer rod filling the rest. This follows ASTM C1193 and is what lets the bead stretch instead of tearing. Filling a wide joint to full depth wastes caulk and makes a weaker seal.