The rafter length calculator works out total expenses, rafter length and roof pitch from roof pitch, installation duration, installation cost, rise, roof length, run, single truss cost, on-center spacing and tan. Enter what you have and the relationship is applied straight away, so you get the answer without working through the algebra yourself.
What Is the Rafter Length Calculator?
The rafter length calculator turns roof pitch, installation duration, installation cost, rise, roof length, run, single truss cost, on-center spacing and tan into total expenses, rafter length and roof pitch, so you can order the right amount of material the first time.
Material estimates are where projects go over budget. Getting the quantities right before the delivery arrives is worth more than any discount on the order.
How to Measure for the Rafter Length
Measure everything in the same unit and take the largest dimension you can reasonably use rather than the average. Formwork, ground conditions and cutting waste all push the real figure above the theoretical one.
Where a plan calls for a specific thickness, check it against local building regulations before you order. The calculator reflects the relationship, not the code.
Allowing for Waste and Errors
Order a little more than the calculation suggests. The gap between the theoretical quantity and what actually arrives on site is normally waste, spillage, over-excavation and uneven grading, and all of it comes out of the same budget.
Write the figures down and compare them with what you actually used on site. That is how you build an estimate you can trust for the next job.
A Worked Example
Working through an example, with roof pitch set to 10, installation duration set to 5, installation cost set to 2, the calculator returns rafter length of 100.12492, and truss count of 3, and total expenses of 16. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out total expenses?
Enter roof pitch, installation duration, installation cost, rise, roof length, run, single truss cost, on-center spacing and tan. The calculator then works through the relationship and reports total expenses, rafter length and roof pitch.
What does the rafter length actually calculate?
It takes roof pitch, installation duration, installation cost, rise, roof length, run, single truss cost, on-center spacing and tan and converts them into total expenses, rafter length and roof pitch using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter roof pitch?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Why does a small change in one value move the answer so much?
That happens when an output depends on a ratio, because dividing by a small number magnifies any change in it. Check the units first, then check whether the value you entered is in the range the relationship was designed for.
Is the answer exact?
It is as exact as the formula and the inputs allow. The method itself is the standard one for this problem, so the only sources of error are the figures you enter and the precision you ask for.