What is pipe bedding and why is it important?

Pipe bedding is the material placed in the trench to support the drainage pipe. Proper bedding distributes loads evenly, prevents point loading that could crack the pipe, and provides a stable foundation. Without correct bedding, pipes can deflect, crack or develop leaking joints.

What are the different bedding classes?

Class D is the most common: 100mm granular bed under the pipe with granular fill to the haunch (halfway up). Class F adds granular fill to 300mm above the pipe crown. Class S is full concrete surround for maximum protection. Class N uses the natural trench bottom where soil is suitable.

What material is used for pipe bedding?

The standard material is 10mm single-size pea gravel (also called pea shingle). It flows easily around the pipe and provides good support. For Class S bedding, C20 concrete is used. Sharp sand can be used as an alternative to pea gravel but must be compacted in 150mm layers.

How wide should the trench be?

The minimum trench width is the pipe outside diameter plus 300mm (150mm clearance each side). For 110mm pipe, this means 410mm minimum — typically dug at 450mm. For 160mm pipe, the minimum is 460mm. Wider trenches are needed for deeper installations or where concrete bedding is used.

How many bulk bags of pea gravel do I need?

Pea gravel weighs approximately 1.6 tonnes per cubic metre. A standard bulk bag contains about 0.5m³ or 0.8 tonnes. Calculate your total volume in m³, multiply by 1.6 to get tonnes, then divide by 0.8 for bulk bags. Always add 10% for waste and compaction.

TradeCalculator

Pipe Bedding Calculator — Granular Bed, Haunch & Surround Volumes

Calculate pea gravel or concrete volumes for pipe bedding classes D, N, F and S based on trench width, pipe diameter and run length.

Pipe Run Length

Total length of drainage pipe

Trench Width

Internal trench width

Pipe Diameter

Bedding Class

Price Per Tonne (optional)

Cost of pea gravel per tonne delivered

How We Calculate This

This calculator determines the volume of bedding material needed based on the pipe diameter, trench width, bedding class and pipe run length.

The formula

Bed Volume = Length × Trench Width × Bed Depth

Haunch Volume = Length × (Trench Width × Haunch Height - Pipe Area)

Total Tonnes = Total Volume × 1.6 (pea gravel density)

Bedding depths

Class D: 100mm bed + haunch to pipe centre
Class F: 100mm bed + 300mm above crown
Class S: Full concrete surround

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.