With so many different drain pipe sizes available, it’s not always obvious which is the correct one for your application. As pipe size is so crucial to the operation of your underground drainage system, we’ve put together this quick guide to various pipe diameters and types to help you quickly find what you need. Across sewage, surface water and potable supply, read on to discover the ideal solution, and if you need further guidance, don’t hesitate to contact the Drainfast team for expert advice.
What are the different drain pipe sizes?
Drain pipes come in myriad sizes to suit different applications, from domestic waste to heavy-duty commercial drainage. Pipe sizes are measured in either ID (internal diameter) or OD (outer diameter). ID refers to the opening inside of a pipe and determines how much liquid a pipe can carry. Let’s break down the most common sizes and where they’re typically used. OD includes the pipe wall thickness, which is important for determining fitting compatibility and external clearances.
110mm drainage pipes
Our 110mm drainage pipes are the most common type used for domestic and lighter-use commercial drainage systems. They are sometimes referred to as 100mm pipes, based on their internal diameter or as 4-inch pipes. Made from durable uPVC, they offer a high flow capacity, easy installation and considerable corrosion resistance. Ideal for soil waste and rainwater discharge, this width of pipe comes in multiple lengths and with fittings to suit any underground drainage layout. Perfect for housing, schools and more, these pipes are light, easy to handle and highly versatile.
160mm drainage pipes
Our 160mm drainage pipes are ideal for larger domestic or small commercial sites, especially where higher flow volumes are needed or gradients are limited. These can be referred to as 150mm pipes based on their internal diameter or 6-inch pipes. Mostly manufactured from strong, corrosion-resistant uPVC (but with other options available), they are lightweight, easy to cut and simple to install. This size is well-suited to shared or surface water drainage systems and features a wide range of compatible fittings to make installation easy.
200mm sewer pipes
Among larger drain pipe sizes, our 200mm sewer pipes are popular for large commercial or high-capacity drainage networks. Built from durable materials like uPVC and polypropylene, they’re ideal for managing wastewater, sewage and surface run-off in heavy-duty systems. Compatible with a range of socketed fittings and reducers, this size offers versatile layout options and long-term reliability for new developments, upgrades and industrial sites, with high resistance to corrosion, chemicals, rot and vermin.
250mm sewer pipes
As one of the larger drain pipe sizes, 250mm sewer pipes are suited to major commercial, industrial or infrastructure projects that need robust flow capacity. Manufactured from strong, long-lasting plastics, they are resistant to corrosion, chemicals and ground movement. This size is ideal for large-scale sewage and surface water systems and supports a wide selection of bends (including 15°, 30°, 45° and 87.5°), junctions and reducers for reliable and long-lasting connections across big layouts.
315mm sewer pipes
As one of the largest standard drain pipe sizes, 315mm sewer pipes are best suited to high-demand systems across commercial estates, infrastructure projects and large-scale surface water drainage needs. Built to withstand high flow rates, they offer strength, flexibility and chemical resistance. With a full range of bends, reducers and junctions, they’re ideal for complex layouts requiring long-term performance and secure, watertight connections under heavy operational loads.
Surface water pipe sizes
We also stock a wide range of BBA-approved twinwall surface water pipes, available in sizes from 150mm to 900mm. These rigid pipes feature a corrugated outer wall for strength and a smooth internal surface for unimpeded flow. Designed for use with non-pressure, surface and sub-surface storm water drainage applications, they’re ideal for culverts, roads, car parks, land drainage systems and more. Supplied in 6m lengths, twinwall pipes are lightweight, easy to install and highly resistant to settlement, making them a strong alternative to traditional concrete systems. We also supply a large variety of twinwall pipe couplers and bends, junctions, reducers and sealing rings.
Water pipe sizes
Our MDPE (medium-density polyethylene), HDPE (high-density polyethylene) and HPPE (high-performance polyethylene) water pipes are available in diameters including 20mm, 32mm and 50mm, lengths including 25m, 50m and 100m and with pressure ratings up to 16 bar. Designed for potable water supply, they are ideal for new connections, mains extensions and any infrastructure upgrades. MDPE and HDPE water pipes are known for their flexibility and corrosion resistance, while HPPE pressure pipes also deliver higher strength for more demanding systems and installations. Lightweight, easy to install and fully compliant with UK standards, these pipes are a reliable choice for domestic and commercial water systems.
Barrier water pipe sizes
Barrier water pipes are designed to prevent the contamination of potable water, especially in contaminated or high-risk ground. Available in sizes including 25mm, 32mm, 63mm and 90mm (typically in 50m coils), they’re ideal for developments on brownfield sites that have hosted refineries, fuel stations and other industrial installations. These pipes feature a protective barrier layer that prevents pollutants from entering the water supply and are also used in heating systems as they prevent oxygen (and other gases) from entering the pipe, extending system lifespan. Options include the Protecta-Line system and SLA systems, with a wide range of fittings available for secure, compliant connections.
What are common drain pipe sizes in the UK?
In the UK, 110mm and 160mm are the most commonly used underground drain pipe sizes, especially for domestic and lighter commercial systems. Larger sizes like 200mm, 250mm and 315mm are used in infrastructure, industrial or high-capacity projects where greater flow rates are needed.
What is the minimum-sized drain pipe allowed underground?
110mm is generally the minimum standard size for underground drainage in the UK, which is commonly used for foul water and waste discharge. Smaller diameters may be used for specific internal or above-ground pipework, but anything underground must comply with Building Regulations and BS EN 1401-1 standards.
How is a drainage pipe measured?
Drain pipe sizes are generally measured by outer diameter (OD), especially for rigid pipes like uPVC types. Inside (or internal) diameter (ID) may be used for more flexible pipe types; check product listings to be sure which is being used. It's essential to check whether OD or ID is being referenced, as fittings and adaptors must be compatible with the correct measurement type to ensure a secure, watertight connection. Length is usually provided in metres. Pipe wall thickness and pressure rating (for pressurised systems) may also be specified, particularly for MDPE, HDPE or barrier pipes.
What factors affect the size of the pipe you buy?
Pipe size requirements can be dependent on several factors, including the volume of water or waste being carried, the gradient of the pipe when installed and also the expected usage of the system – is it a single pipe connecting a sink to a soil stack or part of a larger, shared system further down the line? Larger developments, high-flow areas or shallow gradients typically require wider pipes to avoid blockages. Installation location (inside or outside) and available connection types or fittings may further narrow down the correct size and type of pipe for your project.
Underground drainage systems with Drainfast
We hope this blog post has helped clarify the different drain pipe sizes available and which ones may be more suitable for your intended use. Here at Drainfast, we’ve been providing drainage supplies since 2003 and have built our reputation on our unbeatable service, wide product selection and rapid delivery. If you need assistance or just need your order quickly, we’re here to help you find what you need. Call us today on 01420 555600 or drop us a message, and we’ll steer you in the right direction.
