What Size Is a Drain Plug? It Depends—Here’s How to Know

There isn’t a single standard drain-plug size. In cars, the most common engine oil drain plug threads are metric M12×1.25, M14×1.5, M15×1.5, and M16–M17×1.5; some American vehicles use SAE 1/2″-20 or 5/8″-18. In household plumbing, typical plug/stopper diameters are 1-1/4 in and 1-1/2 in for bathroom sinks and tubs, and 3-1/2 in for kitchen sink strainers. The correct answer for you depends on the application—vehicle make/model or the type of fixture—so verify with a manual or by measuring.

Why there’s no single “drain plug size”

“Drain plug” is a catch-all term covering automotive oil pan bolts, transmission and differential plugs, radiator petcocks, plus plumbing stoppers for sinks, tubs, and marine transoms. Each uses different thread standards, sealing methods, and diameters. Manufacturers choose sizes based on space, materials (aluminum vs. steel pans), and service requirements, which is why the exact size varies widely.

Common automotive engine oil drain plug sizes

These are the sizes you’re most likely to encounter on passenger vehicles; use them as a starting point and confirm against your owner’s/service manual or by measurement.

• Toyota/Lexus: Often M12×1.25 or M14×1.5; many use a 14 mm hex head and a 12 mm or 14 mm crush washer.
• Honda/Acura: Commonly M14×1.5 with a 17 mm hex head; 14 mm crush washer.
• Nissan/Infiniti: Frequently M12×1.25 or M14×1.5 depending on engine family and year.
• Subaru: Often M16×1.5 with a 17 mm hex head; 16 mm crush washer on many models.
• Mazda: Typically M14×1.5 on recent models.
• Hyundai/Kia: Commonly M14×1.5; hex heads vary (14–17 mm).
• Volkswagen/Audi: Often M14×1.5; head can be 19 mm hex or internal hex (6/8 mm) depending on engine.
• BMW/MINI: Frequently M12×1.5 or M14×1.5; some use single-use aluminum or composite plugs—replace each oil change.
• Mercedes-Benz: Commonly M14×1.5 on many engines; some applications use different styles (check by engine code).
• Ford/GM/Ram (US brands): Mix of metric and SAE; very common are M14×1.5 and SAE 1/2″-20 or 5/8″-18 on older models and trucks.
• Motorcycles/powersports: Often M12×1.5 or M14×1.5; torque values are lower than cars—verify carefully.

Even within a brand, engines differ. Treat these as typical patterns, not guarantees. Always match both thread diameter and pitch, and use the specified sealing washer or O-ring.

Typical head/driver sizes and sealing washers

Beyond thread size, the head/driver and sealing method must also match your plug to ensure proper installation and leak-free service.

• Common head/driver sizes: 13 mm, 14 mm, 17 mm, 19 mm hex; internal hex (Allen) 6 mm or 8 mm; Torx (e.g., T45) on some European plugs.
• Crush washer inside diameters typically align with thread: 12 mm (for M12), 14 mm (for M14), 16 mm (for M16). Materials include aluminum, copper, and fiber.
• Some vehicles (e.g., BMW, certain VW/Audi) specify single-use aluminum or composite plugs with pre-fitted seals—replace, don’t reuse.

Using the correct washer is as important as the plug itself. A mismatched washer can cause seepage or require over-tightening, risking pan damage.

Torque guidance

Oil drain plug torque varies by engine and pan material. As a broad reference, many steel pans specify roughly 20–35 lb-ft (27–47 N·m) and many aluminum pans specify toward the lower end of that range. Some trucks call for higher values. Always use the factory specification; overtightening is a common cause of stripped threads and leaks.

Common plumbing drain plug and stopper sizes

For household fixtures, “size” usually refers to the nominal pipe/drain standard or the stopper diameter that fits the opening.

• Bathroom sink (lavatory): Drain assemblies are typically 1-1/4 in nominal. Pop-up or rubber stoppers that fit the opening are commonly about 1-1/4 to 1-3/8 in in diameter.
• Bathtub: Drain shoe threads are typically 1-1/2 in NPSM; most tub stoppers (lift-and-turn, toe-touch) are made to fit that opening. Linkage posts are often 3/8 in or 5/16 in.
• Kitchen sink: The strainer opening is standardized at 3-1/2 in (90 mm). Basket strainers and disposal splash guards/plugs are sized for this opening.
• Utility/laundry sinks: Commonly use 1-1/2 in drains; rubber stopper sizes vary—match to the measured opening.

Because finish flanges and stopper styles vary, confirm both the nominal drain size and the actual top opening before buying a replacement plug or stopper.

Other contexts you might mean by “drain plug”

Outside automotive oil pans and household fixtures, several other systems use drain plugs with different standards.

• Marine transom/garboard: Frequently 1/2 in NPT or 3/4 in NPT threaded plugs; some use expanding rubber plugs sized by bore diameter.
• Differentials/manual transmissions: Common sizes include metric (e.g., M18×1.5) and square-drive plugs (3/8 in or 1/2 in) with sealing washers or tapered threads.
• Radiators: Often plastic petcocks or quarter-turn drains with proprietary threads—replacement is usually application-specific.

These applications are less standardized than they appear. Always identify thread type (parallel vs. tapered) and sealing method before replacement.

How to identify your exact drain plug size

If you don’t have the spec from a manual or parts catalog, a quick measurement routine will get you there reliably.

1. Remove the plug and clean it and the sealing surface.
2. Measure the thread’s outside diameter with calipers (metric in mm; SAE in inches).
3. Determine thread pitch: for metric, measure the distance between peaks (e.g., 1.25 or 1.5 mm); for SAE, count threads per inch (e.g., 18, 20 TPI).
4. Check the head/driver type and size (hex, internal hex, Torx) to ensure tool compatibility.
5. Identify the sealing method: crush washer, O-ring, bonded washer, or tapered thread (NPT).
6. Match a new plug and washer to these measurements or cross-reference your VIN/engine code in a reputable parts catalog.
7. Install with a torque wrench to the factory spec; replace the washer if specified as single-use.

Measuring both diameter and pitch prevents the most common mistake: mixing close-but-wrong sizes that can thread in but won’t seal—or worse, will strip the pan.

Quick purchasing checklist

Before you buy a replacement drain plug or stopper, confirm these points to avoid returns and leaks.

• Thread size/type: e.g., M14×1.5, 1/2″-20, 1-1/2 in NPSM, or 1/2 in NPT.
• Sealing: correct crush washer/O-ring included; replace single-use plugs.
• Head/drive: matches your tools (hex size, internal hex, Torx, square-drive).
• Material/coating: steel, aluminum, composite; corrosion resistance if exposed.
• Features: magnetic tip for engines/diffs if desired; low-profile if clearance is tight.

Matching all five factors ensures the new part fits correctly, seals reliably, and can be serviced easily later.

Summary

There’s no universal drain plug size. For cars, expect common threads like M12×1.25, M14×1.5, M15×1.5, and M16–M17×1.5, with some SAE sizes still in use; for plumbing, bathroom drains are typically 1-1/4 to 1-1/2 in and kitchen sink strainers are 3-1/2 in. Identify your exact application, measure thread diameter and pitch, confirm the sealing method and head style, and tighten to the manufacturer’s torque spec.