At Harpr Surveyors, we strive for accuracy and understanding that measurements are crucial for the area and perimeter calculations of bay windows for energy assessments. This is why we've developed a free, user-friendly Bay Window Calculator to help you get quick and reliable room data - including total area, and perimeter length - with downloadable reports in JPEG and PDF included, great for audit purposes.
The Bay Window Calculator
Why Bay Windows Matter
Bay windows can account for a substantial area percentage when compared with the overall figure and sometimes affect the area if they aren't included, particularly for dwellings with small dimensions. RdSAP Convention 2.01, Measurements states that you are to "Measure all perturbations (e.g. bay windows)..."

What the Tool Does
Our calculator takes just seconds to use and includes the following features:
- Standard Bay Windows – perfect for measuring a trapezoid shaped bay.
- Rounded Bay Windows – great for a quick, accurate figure for a circular bay window.
Download for auditing purposes
After entering your dimensions, you can download a JPEG or PDF report showing your work to be able to upload alongside your other evidence for auditing.
Who Is This Tool For?
This tool has been designed specifically for energy assessors, whether domestic or non-domestic, for free, forever!
Why We Built the Bay Window Calculator
Whether you're a student or a seasoned pro lodging many EPCs, having this tool on your phone, tablet or desktop will narrow down the time it takes to do your manual calculations - it'll also be more accurate than the 'by eye' measurements the accreditation bodies accept.
Save this tool for later
Add this page to your home screen by:
- Tapping the
button in the toolbar - select "Add to Home Screen" from the menu that pops up. You may need to scroll down
Need More Surveying Tools?
We’re developing a suite of tools, including an average ceiling height calculator to help both homeowners and professionals. Stay tuned by visiting our property tools page. Got a suggestion for a tool? Comment below.




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