Free Pipe Sizing & M&E Calculators

The Problem

Engineering shouldn't depend on a spreadsheet

Building services engineers spend too much time hunting through unfamiliar online calculators, recreating spreadsheet formulas, or digging out reference tables. The Mechanical Toolbox gives you one consistent place for every pipe and mechanical calculation you need - no setup, no cost.

Without the Toolbox

Pipe sizing spreadsheets maintained by whoever built them last
Online calculators with no unit control and unclear assumptions
Control valve sizing done by hand from manufacturer datasheets
Pressure drop calculations across multiple disconnected tools
No quick way to check thermal expansion for a new pipe run
Flange bolt torques looked up in BS tables each time
Flow unit conversions done ad hoc with no consistency check

With the Mechanical Toolbox

Pipe diameter, flow rate and velocity calculated instantly in one tool
Consistent unit handling across all 23 tools with clear inputs
Control valve Kv, authority and rangeability all in one place
Darcy-Weisbach and localised losses calculated together
Thermal expansion, loop sizing and restraint force at a click
Flange bolt torque, pattern and gasket check from a single screen
Volumetric flow conversions across l/s, m³/h, UK/US gallons and more

How It Works

Register once. Start calculating immediately.

The Mechanical Toolbox is designed to be useful from the moment you log in. No configuration. No data to import. Just open the tool you need and get your answer.

Create your free account

Register in under a minute through the Construct Software ID system. Your account gives you immediate access to all 23 tools - no credit card, no trial period, no catch.

Open the tool you need

Pick from 23 purpose-built calculation tools covering pipe flow, pump sizing, heat load, ductwork, glycol freeze protection, drainage, fan power, valve sizing, commissioning and more.

Enter your values, get your result

Each tool has a clean, engineer-friendly interface. Enter your known values, select your units, and the result is calculated instantly - with full unit visibility throughout.

The Toolbox

23 tools. Every calculation you need.
Nothing you don't.

Pipe Diameter, Flow Rate & Velocity

Calculate pipe internal diameter, flow rate, or flow velocity. Enter any two of the three values to calculate the third using the continuity equation.

Flow Coefficient (Cv / Kv)

Calculate a valve's flow coefficient (Kv / Cv) from flow rate and pressure drop, or determine flow rate or pressure drop from a known coefficient, for water and other liquids.

Thermal Expansion & Contraction

Calculate thermal expansion in pipework — including change in length, expansion loop leg sizing using the guided cantilever method, and the axial restraint force in a fully fixed pipe.

Heat Load & Flow Rate

Calculate the thermal power transferred in a heating or chilled water system using Q = ṁ × Cp × ΔT, for water or glycol mixtures. Solve for heat load, flow rate, or temperature differential.

Ductwork Pressure Drop

Calculate air velocity, friction factor and pressure drop in circular or rectangular ductwork using the Darcy-Weisbach equation, with the friction factor from the Swamee-Jain approximation to Colebrook-White.

Gravity Drainage

Calculate full-bore flow capacity, required internal diameter, or required gradient for gravity drainage pipes using the Colebrook-White equation (BS EN 12056-2) or Manning's equation, with Approved Document H Table 6 minimum gradient checks for foul drains.

Time to Empty Tank

Calculate the time to drain a tank under gravity using Torricelli's theorem. Supports vertical cylindrical, rectangular, and horizontal cylindrical tanks.

Volumetric Flow Rate

Convert volumetric flow rates between litres per second, litres per minute, litres per hour, cubic metres per hour, and UK/US gallons. Optionally calculate volume discharged over a given time period.

Control Valve Sizing

Size a two-port control valve by calculating the required Kv and comparing the nearest standard sizes, check design and minimum valve authority against CIBSE Guide H, and evaluate rangeability for equal-percentage or linear characteristics.

Pipe Support Spacing

Calculate the maximum support spacing for pipework from pipe material, size, fluid content, insulation and the governing limit (deflection or bending stress). Includes reference tables for copper and steel pipe size series, with BS EN 806-4 recommended spacings for copper.

LMTD & Heat Exchanger Area

Calculate the Log Mean Temperature Difference for counter-flow or parallel-flow heat exchangers, and determine the required heat transfer area from duty, LMTD, and overall heat transfer coefficient.

Fan Power

Calculate the shaft power drawn by a fan from volume flow rate and total fan pressure, or back-calculate flow rate or total pressure from a known shaft power input and efficiency.

Differential Pressure & Head

Convert between differential pressure and equivalent fluid head, and convert pressure values between bar, kPa, mbar, psi, and other common units used in building services.

Nominal Pressure vs Temperature

Look up the maximum allowable working pressure at temperature for flanges (BS EN 1092-1/-2), copper fittings (BS EN 1254) and plastic pipes (PE100, PVC-U, PE-X, PP-R, PVC-C), using published pressure–temperature data.

Pipe Insulation Heat Loss

Calculate the heat loss (or heat gain for chilled pipework) per metre from an insulated pipe, or the insulation thickness needed to meet a target heat loss, using the radial heat conduction equation for a cylindrical shell.

Commissioning Valve Flow Rate

Calculate the flow rate through a commissioning valve from its Kv and a measured differential pressure, the Kv needed for a target flow, or the expected differential pressure at design flow — with a specific gravity correction for glycol mixtures.

Distributed & Localised Pressure Drops

Calculate distributed pressure losses in pipe sections using the Darcy-Weisbach equation (with Colebrook-White friction factor), and localised losses in fittings using Kv or zeta (ζ) coefficients.

Flange Connector Installation

Calculate bolt tightening torque and the star-pattern tightening sequence, look up BS EN 1092-1 flange and bolt dimensions, and check gasket bolt loads to ASME VIII Appendix 2 using standard BS EN 1514-1 gaskets or your own gasket dimensions.

Glycol Freeze Protection

Determine the glycol concentration required for a target freeze protection temperature, or calculate fluid properties — density, specific heat, and viscosity — for a given glycol type and concentration.

Relief Valve Sizing

Calculate the minimum orifice area for a pressure relief valve in liquid service, or the capacity of a known valve, at the relieving pressure (set pressure plus overpressure) using the valve's certified discharge coefficient, as in BS EN ISO 4126-7.

Pump Power

Calculate pump shaft power from flow rate, total head, and efficiency — or back-calculate flow rate or total head from a known shaft power.

Water Hammer

Calculate the pressure surge caused by water hammer using the Joukowsky equation, and determine the minimum safe valve closure time to limit the surge within acceptable bounds.

Expansion Vessel Sizing

Calculate the minimum expansion vessel volume for a sealed hot or chilled water system to BS EN 12828, from system volume, fluid expansion, vessel pre-charge pressure and safety valve setting, including the water reserve.

Who It's For

Built for anyone who designs,
installs or maintains mechanical services

The Mechanical Toolbox covers the calculations that come up day-to-day across the full breadth of building services and mechanical contracting work.

M&E Designers & Consultants

For consultants producing compliant designs

Quickly check pipe sizing, calculate pressure drops, confirm control valve authority and validate thermal expansion calculations during design – without switching between separate tools or spreadsheets.

Pipe flow, sizing and pressure drop checks in a single tool
Control valve Kv, authority and rangeability calculations
Heat load, LMTD and heat exchanger area sizing
Thermal expansion, loop sizing and pipe insulation calculations
Ductwork pressure drop for circular and rectangular ducts
Pump shaft power, head and flow from pump efficiency
Glycol concentration for freeze protection, with fluid properties
Expansion vessel sizing for sealed systems to BS EN 12828

Mechanical Contractors & Site Engineers

For contractors installing and commissioning on site

On-site calculations for pipe support spacing, flange bolt torque sequences, pump power and tank drainage times – available from any device with a browser, without installing anything.

Flange installation torque values and tightening sequences
Pipe support spacing reference tables by material and size
Gravity drainage capacity and gradients with Approved Document H checks
Fan power, relief valve sizing and commissioning calculations
Darcy-Weisbach distributed pressure losses with localised Kv/zeta additions
Commissioning valve flow rate from measured differential pressure
Tank drainage times for vertical, rectangular and horizontal tanks
Volumetric flow conversions across l/s, l/min, m³/h and UK/US gallons

Construct Software Ecosystem

Part of a broader suite of
specialist engineering tools

The Mechanical Toolbox sits alongside a growing suite of Construct Software products covering cable calculation, test and certification, compliance management, facilities management and more - all built specifically for the MEP sector.

ElectraCert

BS 7671 test & certification software for EICs, EICRs and Minor Works

CableSpec Pro

BS 7671 cable calculation for single circuits and multi-circuit projects

SafetyCert

Compliance management platform for PAT testing, Minor Works and EICRs

ContractorCompliance

Contractor insurance, accreditation and competency management

FacilitiesMaster

Full-stack FM platform for PPM, assets and compliance documentation

InterimReport

Structured electrical interim inspection reports and checklists

TESCert

BS 7909 temporary electrical system certification for events and media

More coming

The Construct Software suite continues to grow with new specialist tools

Learn more at our About page or visit constructsoftware.co.uk.

FAQ

Common questions answered

Everything you need to know before getting started.

Who is the Mechanical Toolbox for?

The Mechanical Toolbox is designed for anyone working in building services, M&E design, mechanical contracting or facilities management who regularly needs engineering calculations. This includes design engineers and consultants, mechanical contractors, site engineers, project managers and students learning building services engineering. If you work with pipework, pumps, valves, heat transfer or mechanical systems in buildings, the Toolbox has tools you will use.

Is it really free?

Yes. The Mechanical Toolbox is offered entirely free of charge as part of the Construct Software ecosystem. There is no trial period, no subscription, no credit card required and no premium tier. All 23 tools are available to every registered user at no cost. The Toolbox is funded by Construct Software's broader product portfolio.

Do I need to install anything?

No. The Mechanical Toolbox is a cloud-based web application. You access it through any modern web browser on a desktop, laptop or tablet - no installation, no plugins, no app store. Just log in and start calculating. An internet connection is required.

What engineering standards do the tools reference?

The tools are built around the standards and methods commonly used in UK building services engineering, and each tool states its sources. Examples: pipe support spacing combines a beam calculation with the BS EN 806-4 recommended spacings for copper, and follows the BESA TR 50 approach of using manufacturers' data first. Flange dimensions, bolt patterns and pressure ratings reference BS EN 1092-1, with gasket factors from ASME BPVC VIII-1. Control valve authority follows CIBSE Guide H. Drainage uses the Colebrook-White equation (BS EN 12056-2) with Approved Document H checks, and pressure losses use the Darcy-Weisbach equation with the Colebrook-White friction factor. Where a value comes from a secondary or manufacturer source rather than a standard, the tool says so.

How accurate are the calculations?

The calculations use established engineering equations and published data - Joukowsky for water hammer, Torricelli for tank drainage, the continuity equation for pipe flow, the Darcy-Weisbach equation with the Colebrook-White friction factor, and so on. Reference data is taken from the standards and manufacturer documents named in each tool; where a value is secondary, generic or unconfirmed, the tool labels it. The tools are intended to support engineering judgement and design work, not to replace it. You should always validate results against project-specific conditions and applicable standards.

Is my account data secure?

Account authentication is handled by the Construct Software ID system, which uses cryptographically hashed credentials, secure session management and cross-subdomain cookie validation. The Mechanical Toolbox itself stores only a small amount of user preference data (your most recently viewed tool). No sensitive personal or project data is stored within the Toolbox application.

Can I use it on a phone or tablet?

The Mechanical Toolbox is designed primarily for desktop and tablet use, where you can comfortably enter values and read results on a full-size screen. It is accessible on mobile but the calculation interfaces work best on a screen of 768px width or wider.

Free building services calculators,right in your browser.