Harth / Free tools
Drawing & geometry
These seven calculators cover the geometry that comes up while drawing and checking a building: scale conversion between drawing and real dimensions, mixed feet-and-inch arithmetic, roof pitch and sloping area, ramp gradient, straight-flight stair risers and treads, floor and wall areas with openings, and an occupant load worksheet driven by the factors you supply.
7 drawing & geometry tools
Free export on every toolArchitectural scale calculator
Move between drawing and real dimensions, resize a print, and export a scale bar.
Interactive tool · Free exportRoof pitch & roof area calculator
Convert roof pitch and total the sloping area and covering strips of your roof planes.
Interactive tool · Free exportRamp gradient calculator
Convert rise and run to gradient, angle and sloping length.
Interactive tool · Free exportStair geometry calculator
Find straight-flight riser and tread options using your own design limits.
Interactive tool · Free exportOccupant load & egress worksheet
Calculate occupant loads and width allowances using factors from your chosen code.
Interactive tool · Free exportFeet, inches & construction units
Add mixed feet-and-inch lengths and convert length, area, volume and mass.
Interactive tool · Free exportFloor & wall area calculator
Total rectangular floor zones, wall faces and openings with a labelled plan.
Interactive tool · Free exportAbout the drawing & geometry tools
Every calculator opens with a worked example in imperial units and switches to metric with one control. The choice is remembered across all of the free tools in your browser. Inputs are converted with exact factors before the calculation runs in SI, so the imperial and metric results agree to the displayed precision.
Each page shows its formulas beside the inputs and explains its assumptions and limits. The stair and ramp tools compare options against the limits you enter rather than applying a fixed code; the occupant load worksheet records the code source, edition and factors you chose. Results export as PDF or CSV, and calculator inputs can be saved as a local JSON file and reopened later.
Nothing is uploaded. The tools run entirely in the browser, without an account or a usage limit.
Start with: Architectural scale calculator, Roof pitch & roof area calculator, Stair geometry calculator.
Popular questions
What ratio is 1/4 inch = 1 foot?
1/4" = 1'-0" is 1:48. One foot is twelve inches, and 12 ÷ 0.25 = 48, so every quarter inch on the drawing represents 48 quarter inches, or one foot, in reality.
From the Architectural scale calculator
What is a 6/12 roof pitch in degrees?
A 6/12 pitch is 26.57°. It rises 6 in for every 12 in of horizontal run, which is a 50% slope, and its roof area is 1.118 times its plan area.
From the Roof pitch & roof area calculator
How long does a ramp need to be for a 24 inch rise?
At the ADA maximum slope of 1:12, a 24 in rise needs at least 24 ft of horizontal run, plus 5 ft landings at the top and bottom. The sloping length is 24.08 ft.
From the Ramp gradient calculator
How many stairs do I need for a 9 foot floor-to-floor height?
At the 2021 IRC maximum riser of 7-3/4 in, a 108 in height needs 14 risers of 7.71 in and 13 treads. Under the 2021 IBC's 7 in maximum it needs 16 risers of 6.75 in.
From the Stair geometry calculator
How do you calculate occupant load?
Divide the floor area of each space by the occupant load factor for its use, round up, and add the spaces together. A 1,000 ft² classroom at 20 ft² net per person has an occupant load of 50.
From the Occupant load & egress worksheet
Other free tool categories
- BIM & files4 tools
- Materials & quantities10 tools
- Site & solar3 tools
- Building performance4 tools
- Documents & presentation5 tools
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