M&E calculators

16 M&E calculators: cable sizing, voltage drop, circuit load and breaker, derated current capacity, lighting, water demand, pipe sizing, drainage falls, pump head, heat load, duct area and supports.

16 tools, most used first

◌Water Demand CalculatorPeak day and peak hour demand, with pipe and tank sizing.⌇Cable Size CalculatorDesign current from load, then the conductor size to carry it.↯Voltage Drop CalculatorPercentage voltage drop with a 5% compliance check.◫Circuit Load and Breaker CalculatorDesign current, breaker loading and suggested ratings.≋Cable Ampacity Derating CalculatorTemperature, installation and grouping derating in one step.☀Lighting Level and Fixture CalculatorLumen method fixture count, achieved lux and power density.⊘Water Pipe Sizing CalculatorBore from flow and velocity, with actual velocity and friction loss.⟍Drainage Pipe Slope CalculatorStandard slope by diameter, fall over the run and velocity check.⇡Pump Head CalculatorStatic lift plus losses, giving total head and shaft power.♨Heating Load CalculatorLoad, radiator sections, fuel use and running cost.▭Duct Area CalculatorDeveloped area for rectangular or round duct, plus insulation and steel weight.⌐Duct Support CalculatorBracket count, steel weight, rod weight and anchors in one go.⊟Cable Tray CalculatorTray, bracket and rod weights together with the bracket count.⌇Conduit and Wiring CalculatorConduit, wire and copper weight per circuit, all at once.⌶Pipe Support CalculatorRun length and spacing give bracket count and steel weight.◍Fire Water Tank CalculatorIndoor plus outdoor plus sprinkler, converted to tank volume.

What this group solves

Building services take off along two chains. Electrical is a three-stage check — current capacity, then protection, then voltage drop; picking a cable size is not the end of it, because long runs usually fail on the 5% drop limit rather than on current. Plumbing and HVAC are flow, diameter, then resistance: supply pipe size from fixture units and diversity, drainage from discharge units subject to minimum falls.

The bulk of installation labour hides in supports and accessories: duct hangers spaced by duct width, tray brackets by span, pipe brackets by diameter and temperature. These invisible items routinely account for more than 30% of installation labour, so the tools here return bracket counts, steel weight and anchor counts instead of leaving it to guesswork.

FAQ

How do I choose a cable size?

Calculate design current — I = P / (√3 × U × cosφ) three-phase or I = P / (U × cosφ) single-phase — select a size from the current-carrying table with 1.2-1.5 times margin, then check voltage drop against 5%. On long runs the drop check governs, not the current rating.

How is supply pipe diameter sized?

Convert fixture units to a design flow rate, then size for economic velocity: 0.8-1.5 m/s up to DN50, 1.0-2.0 m/s above. Too fast and you get noise and water hammer, too slow and you waste pipe. Then confirm the pressure at the most unfavourable outlet still meets the minimum working pressure of the fixture.

How is duct surface area calculated?

For rectangular duct, 2 × (long side + short side) × length; for circular duct, π × diameter × length. That is the bare duct development, excluding flanges, stiffeners and insulation. Insulation area is measured separately on the insulated outside perimeter.

Related data tables

Pipe size chart (DN to inch)DN15 to DN300: the inch equivalent, outside diameter, common wall, weight per metre and external area for insulation take-off.

Other groups

Concrete Rebar Masonry Finishes Earthwork Temporary Works Construction Costing Material weights Area and volume Unit conversion Code Lookup

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.