What is the Standard Size of a Tub Drain? The Complete Guide

If you‘re replacing an old tub or installing a new one, choosing the right drain size is crucial. An improperly sized drain can lead to slow water drainage, flooding, and damage. As an expert with over 10 years of experience in home renovation, I‘ve seen the problems bad drainage can cause. This comprehensive guide will provide everything you need to know about standard tub drain sizes, along with tips for measuring, choosing, and installing the correct drain.

Table of Contents

• Overview of Standard Tub Drain Sizes
• Measuring an Existing Tub Drain
• Matching a New Tub Drain
• Common Drain Materials and Features
• Drain Installation Best Practices
• Tub Drain Positioning and Layout
• Connecting Drains to Plumbing
• Troubleshooting Improper Drain Sizing
• Tub Drain Alternatives and Custom Sizes

Overview of Standard Tub Drain Sizes

Most bathtub drains in the US are 1 1/2" in diameter. This size is referred to as a "2 inch drain" in the plumbing world, accounting for the strainer size.

Standard bathtub drain sizes:

• Drain diameter (opening size): 1 1/2"
• Drain body diameter (pipe): 1 1/4" – 1 1/2"
• Total drain assembly height: 4" – 14"

According to the International Plumbing Code (IPC), 1 1/2” is the standard drain diameter size for residential bathtub fixtures. This size is suitable for most modern tubs from major manufacturers like Kohler, American Standard, and Delta.

Older homes may have 1 1/4” drains, while some vintage clawfoot or freestanding tubs use 2” drains. However, for new installations, 1 1/2” is the standard size that fits modern bathtubs and residential plumbing connections.

It‘s crucial your drain diameter matches your plumbing for proper drainage and ventilation. Continue reading for tips on measuring your specific tub and choosing the right drain.

Measuring an Existing Tub Drain

If you‘re replacing a tub drain, it‘s important to measure your existing drain correctly to find the right size replacement. Follow these steps:

Measure Drain Diameter

• Remove the drain cover/strainer plate with a wrench
• Use a ruler or tape measure to measure the diameter across the drain opening
• This is usually 1 1/2", but double check for accuracy, as older drains may be 1 1/4"

Measure Drain Height

• Measure from the tub bottom up to the drain flange/rim
• Include any sections sticking out like an overflow tube
• Height ranges from 4-14 inches

Measure Distance from Tub Edge

• Measure straight out from tub edge to drain center
• Standard distance is 5-6", but verify your tub specifications
• Freestanding tubs may be 7-9"

Match these measurements as closely as possible when choosing a replacement drain. Having the exact diameter size is most crucial for proper fit and water flow.

Matching a New Tub Drain

Follow these tips when selecting a drain for a new tub installation:

• Confirm the tub drain hole size (may be 1 1/4", 1 1/2", or 2")
• Choose a drain with matching diameter for proper fit
• Consider a slightly larger diameter if the tub floor is higher
• Account for any thick tile, mortar bed, or plumbing modifications
• Ensure total drain length fits tub depth and existing drain height

I recommend getting the drain hole diameter from the tub manufacturer if possible. For example, Kohler notes the drain hole size in their tub spec sheets.

Look for a drain with an adjustable or telescoping height if your measurements don‘t align perfectly. This provides flexibility during installation.

Common Drain Materials and Features

Tub drains are available in a range of materials and designs. Consider the following:

Materials

Plastic (PVC)

• Lightweight and affordable
• Durability can vary by brand
• Budget-friendly option

Brass

• Very durable material
• Available in polished, brushed, or oil-rubbed finishes
• Decorative accent for vintage or high-end bathrooms

Stainless Steel

• Modern aesthetic appeal
• Resistant to corrosion and tarnishing
• Provides durability

Features

Pop-up

• Simple push-pull plunger mechanism
• No trip lever needed
• Most common and affordable option

Toe-tap/Trip lever

• Foot pedal actuator located on tub rim
• Hands-free and easy to use
• Ideal for bathrooms with limited space

Flip-it

• Flip drain up to open and down to close
• No need for a traditional trip lever
• Sleek, contemporary style

Hair catchers

• Built-in strainers prevent clogs
• Great for tub/showers prone to clogs
• Some have easy removable screens

Choose the right mix of material and features for your budget and bathroom needs.

Drain Installation Best Practices

Proper installation is key to ensuring your tub drain works effectively for years to come. Here are my top tips as a professional:

• Use plumber‘s putty around the drain flange for a watertight seal
• Hand tighten flange bolts first, then use a wrench to finish tightening evenly
• Avoid over-tightening bolts to prevent cracking the tub
• Ensure drain is aligned squarely under the tub faucet
• Use a tub support or helper to avoid shifting during install
• Pitch horizontal drain pipes at 1/4" per foot minimum slope
• Install a p-trap close to the tub drain to prevent sewer gas odors
• Avoid using 90 degree elbows in drain lines (use two 45‘s instead)

Consider hiring a professional if you‘re unsure of any part of the installation process – correctly aligning and securing the drain is crucial.

Tub Drain Positioning and Layout

Proper drain placement helps ensure quick water drainage. Follow these guidelines:

• Distance from tub wall: 5-7 inches is standard
• Drain should be centered along tub width
• Position the drain so the trip lever (if applicable) is accessible
• Check manufacturer specs for freestanding tubs
• Adjust drain location if tub will have a mortar bed or tiles
• Test drain location with tub filled prior to finishing plumbing

Getting the drain position right is easier with two people – one to hold the tub steady and level, and one to adjust the drain fittings.

Connecting Drains to Plumbing

Choosing the right pipe size and layout is critical for a functional drainage system:

Recommended drain pipe sizes:

• 1 1/2" pipe for standard bathtub drains
• 2" pipe for larger tubs and distant drain locations
• Use a p-trap close to the drain to prevent gas and odors

Layout considerations:

• Slope horizontal runs at 1/4" per foot minimum
• PVC and ABS are common drain pipe materials
• Avoid 90 degree elbows – use two 45‘s instead for turns
• Limit horizontal run distance to 5-6 feet if possible
• Install cleanouts for access to pipes if needed

Ensure your plumber follows manufacturer specifications for pipe sizes and installation. This helps avoid potential flow problems.

Troubleshooting Improper Drain Sizing

Issues caused by an improperly sized drain include:

• Slow drainage: Clogged drain, sagging pipe, or incorrect slope
• Gurgling noises: Improper venting or p-trap placement
• Leaks: Damaged drain flange seal or loose connections
• Overflow: Drain pipe too small for tub volume

Fixes may involve snaking or replacing clogged pipes, adjusting traps, resealing the flange, or replacing undersized pipes. Complete drain replacement may be needed in severe cases. Consult a professional plumber if you have persistent issues.

Tub Drain Alternatives and Custom Sizes

For atypical tub shapes or sizes, custom drains are an option:

• Slot drains: Narrow linear drains for modern style tubs
• Extra large drains: 3-4 inch drains for huge soaker tubs
• Overflow cover plates: Convert overflow drain to standard size
• Expanded flanges: Allow 1 1/4" drain to fit 1 1/2" hole

Carefully measure your unique tub and consult a plumbing professional to determine if a specialty drain is needed. Custom drains can solve fit issues, but may cost more.

Conclusion

Choosing and installing the proper tub drain takes careful measurement, plumbing knowledge, and attention to detail. I hope this comprehensive guide provides the information you need to select the right drain size and avoid problems. Let me know if you have any other questions – I‘m happy to help!