The pipe is the part nobody forgets
Sticks divide out of the developed length and everybody gets that right. What goes wrong is downstream of it. A coupling at every joint means one fewer than the number of sticks, unless the pipe you buy already has a coupling on each length, in which case you need none and the count is still worth knowing because it tells you how many joints exist. Straps are the ones that get counted on the drive home: one at each end of the run plus one at your working spacing along it, and then another near each box and body if that is how you are working.
The developed length is the other quiet trap. It is measured along the pipe, following every offset, every rise and every jog around an obstruction. Point-to-point across a room is always shorter, sometimes by a lot on a run that has to climb a wall and cross a ceiling. Getting that measurement from a plan rather than a tape is how a run ends up one stick short with everything already strapped up.
Temperature swing is not weather
The expansion arithmetic multiplies three things: the coefficient for the material, the length in inches, and the temperature change the pipe itself experiences. That last one is the one people get wrong, and they get it wrong by using the weather.
A run of dark PVC on a south wall in direct sun does not sit at air temperature. It sits well above it during the day and drops to air temperature at night, so its own swing across a year is considerably wider than the range a weather station records. A run through a conditioned building swings by almost nothing at all. A run that goes outside, crosses a roof and comes back in has two different swings along its length and the outdoor portion governs. The same hundred feet of pipe can want an expansion fitting in one location and none in another, and the only difference is where it happens to be mounted.
PVC moves several times as far as steel for the same swing, which is why expansion fittings are so much more common on plastic runs. The comparison across materials for a length of pipe is worked through on the pipe expansion calculator, which covers the same physics for plumbing pipe and hanger spacing; this page counts the fitting rather than repeating that.
Conduit bodies earn their keep on the pull, not on the plan
A pulling elbow or an access fitting is a small item on a material list and a large item on a difficult pull. A run with several bends builds tension multiplicatively — each bend multiplies everything behind it — so breaking that run into two pulls at a body in the middle does not halve the tension, it collapses it, because the second pull starts from nothing again instead of from whatever had accumulated.
The cable pull tension calculator makes that visible: run the whole sequence, then run the two halves separately, and the difference is usually startling. It is often the cheapest change available on a run that looks marginal, and it costs one fitting.
What is deliberately not here
| Question | Where it belongs |
|---|---|
| How many conductors fit in the pipe | Conduit fill calculator, or the low-voltage pathway calculator for cables given by outside diameter |
| Cubic inches a box needs | Box fill calculator |
| What size conductor to run | Wire size calculator and voltage drop calculator |
| Where the offset marks go | Conduit bend and offset calculator |
| Strap spacing, fill percentage, bend radius minimum | The code your jurisdiction has adopted, and the inspector |
Before anything is opened up
Anything that involves opening ground for a raceway starts with having the underground utilities located. Call 811 or file the online locate request; it is free in the United States and it exists precisely for this. Concealed services inside a building are the same problem with worse lighting.
This page does not supply limits and cannot judge yours. Fill percentages, support and strap spacing, minimum bend radii, tray loading rules, cover depths and every other installation limit come from the code your jurisdiction has adopted and from the manufacturer of the product you actually bought, and the two do not always agree. The arithmetic here runs on figures you type in. Whether the result is acceptable is a conversation with a licensed electrician and with the inspector who signs the job off.
Questions people ask
How many couplings do I need for a run of conduit?
One fewer than the number of sticks, when the pipe comes bare. A 120 foot run in ten foot lengths is twelve sticks and eleven joints between them, so eleven couplings. If the sticks you buy already carry a coupling on one end, you need none as separate items — the calculator still shows the joint count, because that is what tells you how many places the run can leak, pull apart or fail to make continuity.
What strap spacing should I use?
Whatever the code adopted in your jurisdiction requires for that raceway type and trade size, in that orientation, fastened to that surface. This page will not name a figure, because the figure differs between raceway types and between code editions and the one that governs is the one your inspector is reading. Put your own number in the field and the count follows from it.
How do I know if the run needs an expansion fitting?
The calculator gives you the movement — coefficient times length in inches times the temperature swing — and divides it by the travel of the fitting you are buying. What it will not do is tell you whether a fitting is required, because that is the adopted code and the fitting manufacturer instructions together. What is worth getting right on your side is the temperature swing: use what the pipe itself experiences, which for a dark run in sun is considerably more than the air around it, and for a run inside a conditioned building is close to nothing.
Why is my measured run longer than the distance between the two ends?
Because conduit follows a path and the tape across the room does not. Every offset around an obstruction, every rise up a wall, every jog to clear a beam adds length that a straight-line measurement does not see. That is what developed length means, and it is the figure this take-off wants. Pulling it from a plan rather than walking it with a tape is the usual reason a job finishes one stick short.
Does the calculator include prices?
Only yours. The price fields are blank on purpose and the cost section stays hidden until you fill them in, because material prices move constantly and vary by supplier, region and quantity, and a number baked into a web page would be wrong by the time you read it. Put your quoted figures in and the line items and the total are calculated in whole cents so they add up exactly.