Craft Quantities
Plan & Takeoffs

By trade

Electrical calculators

Electrical work is estimated in limits rather than quantities. The answer to almost every question here is a maximum — a current a cable may carry, a drop a run may lose, a fill a conduit may take — and the design is whatever fits inside all of them at once.

  • 46Calculators
  • 3Parts of the site

How electrical is measured

Amperes for loads and ratings, millimetres squared or AWG for conductors, percentages for voltage drop, and counts for everything installed. Lighting is a different unit again: lux on a working plane, from which luminaire count and spacing follow.

Where electrical sits on this site46 across 3
46

Electrical24

Materials & Quantities21

Auto/Utility1

What gets left off a electrical order

  • Derating. A cable's rating assumes conditions — grouping, ambient temperature, insulation — that a real installation rarely matches.
  • Voltage drop on long runs, which routinely forces a larger conductor than the current alone would need.
  • Containment fill: a tray or conduit sized on cable area with no room to pull, or to add a circuit later.
  • Earthing and bonding, which is its own set of conductors and is sized by a different rule from the circuits it protects.

Job takeoffs7

Where electricians meet the rest of the job: each runs one of these calculators, with every other trade in the same job beside it.

Worked examples1

A real job estimated step by step, with this trade's steps counted.

Comparisons8

Two ways of doing the same work, weighed against each other.

Planners2

Work this trade out from a space rather than from a job.