RoofJacker – Roofing Ready Reckoner

Roofing Ready Reckoner App

Online web app for calculating roofing dimensions
Skip to the app – CLICK HERE

RoofJacker - Roofing Ready Reckoner


While teaching at my local technical college, I realised that the popular book of Roofing Ready Reckoner look-up tables had been in use for decades. I felt that it was surely time for a change, from the old and outdated ready reckoner table.

RoofJacker Development

Working together with my son in March 2011, the result was a spreadsheet that he soon coded into HTML. This in turn became a single page web app, which allows you to enter just 3 measurements and calculate all the dimensions you need to construct a roof.

Online Roofing Ready Reckoner

This online Roofing Ready Reckoner app, is a custom coded trigonometrical calculator. This roofing calculator will work on any device with web access and is designed to replace the unwieldy hard copy look-up tables that are also known as the Roofing Carpenter’s Ready Reckoners. These are used to calculate the various angles and measurements required when building a roof.

Roof Ready Reckoner Calculator

With just three measurements, you will be able to use this online Ready Reckoner and calculate the following roofing dimensions; Rise per metre Run, Rafter Length, Hip Length, Jacks Diminish, Common Rafter Seat Bevel, Common Rafter Ridge Bevel, Hip or Valley Seat, Hip or Valley Ridge, Jack Rafter Edge and Purlin Edge.

RoofJacker – Roofing Ready Reckoner

The RoofJacker Ready Reckoner (v1.484) on this page is designed to be a responsive web app. This calculator will work on desktop, tablet and mobile devices; be they iPhone or Android. So it is suited for use when you’re in the office, at college or on site.

How To Use RoofJacker Ready Reckoner

Simply input your measurements for Pitch, Run and Centres, then click “Calculate” and let RoofJacker do the hard work and ready reckoning for you!

Roofing Ready Reckoner App

Enter your measurements:

Pitch: Run: Centres:


  • Rise per metre Run:
  • Rafter Length:
  • Hip Length:
  • Jacks Diminish:
  • Common Rafter Seat Bevel:
  • Common Rafter Ridge Bevel:
  • Hip or Valley Seat:
  • Hip or Valley Ridge:
  • Jack Rafter Edge:
  • Purlin Edge:

To download as PDF click this icon once, it may take a few seconds:

RoofJacker v0.484 © 2011 MC2
RoofJacker v1.484 © 2018 Neon Saw
Comments welcome at
Disclaimer: RoofJacker is currently provided for free, as is.
Neon Saw accepts no responsibility for errors, however caused.