Last checked
May 22, 2026
We checked the page logic, support notes, and related links on this page.
Project planner
Plan the full trench build-up before you order
Drainage quotes are easier to compare when the trench is split into pipe, bedding, gravel surround, membrane, fittings, spoil, and reinstatement instead of one broad allowance.
5 linked calculatorsScope checklistProject sequence
drainage trench calculatordrainage materials calculatorpipe bedding calculator
How to use it
Planning before buying
Use this planner to keep the measurements, material list, and quote scope aligned before anyone prices the work.
Why trust it
See how the site is maintained
Read the calculator methodology and editorial policy for the standards behind these pages.
Measure first
Take these measurements once, then reuse them through the calculators so the order, budget, and quote request stay aligned.
- Full trench length
- Pipe stock length
- Bedding width and depth
- Gravel surround width and depth
- Membrane wrap and overlap
Planning order
Work through the job in this order so the visible finish, hidden layers, accessories, and cost checks are not priced as separate guesses.
Step 1
Map the trench run
Measure the full route, then mark bends, inspection chambers, branches, outlets, and any section that widens around a connection.
Open Drainage Pipe CalculatorStep 2
Calculate bedding below and around the pipe
Price the bedding layer on its own. It may be a sand or pea gravel bed, and it should not be confused with the larger surround or backfill volume.
Open Pipe Bedding CalculatorStep 3
Size the drainage gravel envelope
For a French drain or gravel surround, calculate the trench width and filled depth after the pipe position and membrane wrap are known.
Open French Drain Gravel CalculatorStep 4
Check membrane coverage
Include wrap, overlap, turn-ups, and trimming around chambers before choosing the roll count.
Open Geotextile Membrane CalculatorStep 5
Check any compacted base material
Only include Type 1 where the trench reinstatement, driveway edge, or base repair actually needs a compacted layer.
Open MOT Type 1 CalculatorCalculators in this plan
Each calculator covers one decision in the job: quantity, coverage, depth, fixings, accessories, or budget. Keep the outputs together when you build the buying list.
Step 1Drainage
Drainage Pipe Calculator
Estimate drainage pipe lengths, stock pieces, waste allowance, and practical buying totals for trench runs before you order fittings and chambers.
Open calculatorStep 2Drainage
Pipe Bedding Calculator
Estimate pipe bedding volume, tonnes, and bulk-bag buying quantities for drainage trenches before you order sand or gravel.
Open calculatorStep 3Drainage
French Drain Gravel Calculator
Estimate french drain gravel volume, tonnes, bulk bags, and practical trench-fill buying totals before you order aggregate for the run.
Open calculatorStep 4Drainage
Geotextile Membrane Calculator
Estimate geotextile membrane rolls, overlaps, and covered area for driveways, french drains, trenches, and separating aggregate layers.
Open calculatorStep 5Aggregates
MOT Type 1 Calculator
Estimate MOT Type 1 volume, tonnage, bulk-bag buying quantities, and rough delivery needs for driveways, paths, and compacted sub-base layers.
Open calculatorMaterial checklist
Treat this as the first pass at the buying list. Add product names, sizes, grades, and exclusions before sending it for a price.
- Drainage pipe
- Pipe bedding
- Drainage gravel
- Geotextile membrane
- Fittings and chambers
- Backfill and reinstatement materials
Common mistakes
These are the places where tidy measurement maths often breaks once products, delivery, site access, and labour are involved.
- Counting straight pipe but not fittings
- Confusing bedding with full gravel surround
- Forgetting membrane wrap at corners and outlets
Brief to send for pricing
Show pipe length, bedding, gravel surround, membrane, fittings, chambers, spoil removal, reinstatement, access, and any assumed trench depth as separate quote lines.
Guides worth checking
These pages cover the details that usually decide whether the calculator output is safe to order against.
Guide
Drainage Pipe Length Calculator
Work out drainage pipe lengths from trench run, stock size, and a realistic allowance for bends, cuts, and spare pipe.
Guide
Pipe Bedding Calculator by Volume
Estimate pipe bedding volume for drainage trenches, including practical depth, tonnes, and bulk-bag thinking.
Guide
French Drain Gravel Calculator by Volume
Work out french drain gravel volume from trench length, width, depth, and realistic trench overage before you order.
Guide
Geotextile Membrane Buying Guide
Work out how much geotextile membrane you need, then sense-check overlaps, roll coverage, and groundwork use cases.
Related project plans
Open one of these when the job touches another surface, base layer, finish, or outdoor area.
Related workflow6 calculators
Driveway Base Planner
Driveway base costs rise or fall on depth, compaction, membrane, delivery access, and the difference between fill and finished surface material. Plan those layers before comparing quotes.
Related workflow6 calculators
Patio Planner
A patio order is more than a slab count. Work from the finished area into slabs, Type 1, bedding sand, jointing, edge details, and budget checks before anything is ordered.
Related workflow6 calculators
Garden Surface Planner
Garden surface jobs often mix lawn, soil, seed, bark, membrane, edging, and decorative gravel. Separate the areas before buying materials or asking for landscaping quotes.
Practical answers
Short answers for the decisions that usually come up before ordering materials or sending a quote request.
Is pipe bedding the same as french drain gravel?
No. Bedding supports the pipe; gravel surround or french-drain fill may be a larger volume around it.
What should I measure before pricing drainage?
Measure the trench run, bedding zone, gravel zone, membrane coverage, and fitting or chamber count.
What is the easiest drainage item to miss?
Fittings and chambers are often missed because the first estimate starts with the straight pipe run instead of the actual trench route.