Free homeowner tool
Sketch your extension.
Sketch your extension.
See what it adds.
Upload an existing floorplan, set a known dimension and develop your extension floor by floor. Add levels, use the floor below as a faded reference, annotate dimensions and explore approximate added floor area and build cost.
Your plan stays on your device.
Nothing you upload is sent to ArcForma. The planner runs locally in your browser.
Drop your existing floorplan here
or use the upload button on the left
How to use it
Need help instead? →
Three quick steps.
Upload + calibrate
Use an existing estate-agent, survey or measured plan. Click two points with a known distance so the tool understands scale.
Sketch + annotate
Draw the Ground Floor, then add First Floor or higher levels as needed. The level below stays visible as a faded reference while you align the upper floor.
Explore area + cost
See the area for each level and the total added floor area across the project, then export a multi-level study to keep or use in an initial conversation.
Important: This is an early feasibility tool, not architectural advice or construction information. It does not check title constraints, planning policy, permitted-development rules, structure, drainage, fire safety, Building Regulations or site-specific conditions.