Scale Drawing Calculator

A scale drawing is a drawing where every measurement is reduced (or enlarged) by a consistent ratio — the scale. For example, at 1:100 scale, every 1cm on the drawing represents 100cm (1 metre) in real life. Scale drawings are used in architecture, engineering, and construction so that large real-world objects can be represented accurately on a page.

1:100 means that 1 unit on the drawing equals 100 units in real life. So 1cm on the drawing = 100cm = 1 metre in real life. A wall that is 5 metres long would appear as 5cm on a 1:100 scale drawing. This is one of the most commonly required scales for planning applications, building permits, and zoning submissions.

Requirements vary by country and drawing type. In the US, building permit drawings are often required at 1/4" = 1' (roughly 1:48) or 1/8" = 1' (roughly 1:96). In the UK, planning applications typically require site location plans at 1:1250 or 1:2500, and floor plans or site plans at 1:100 or 1:200. In most of Europe, 1:100 and 1:50 are standard. Always check the specific requirements of your local planning authority, municipality, or building department.

Metric units (metres, centimetres, millimetres) are all powers of 10, so scaling is just a matter of moving a decimal point. Imperial units are messier: there are 12 inches in a foot, so dividing a measurement in feet and inches by 100 requires converting to a single unit first, then dividing, then converting back. For example: 32 feet at 1:100 scale. 32 feet = 384 inches. 384 ÷ 100 = 3.84 inches. That's not a number most people can work out in their head. This calculator does it for you.

Enter the real-world length of whatever you want to measure — a wall, a room, a plot of land. Select the unit (metres, centimetres, millimetres, feet and inches, or inches). Choose a scale from the dropdown, or select Custom to enter your own. Click Calculate. The result shows you how long that measurement should appear on your scale drawing. You can switch the output unit using the dropdown next to the result.

Yes. Just swap the scale ratio. If you measured 3.2cm on a 1:100 drawing and want to know the real-world size, enter 3.2cm and set the scale to 100:1 (using the Custom option). The result will be 3.2 metres.

The UK planning system commonly uses: 1:1250 and 1:2500 for site location plans (based on Ordnance Survey maps); 1:500 for block plans showing the site boundary; 1:100 and 1:200 for floor plans, elevations, and sections; and 1:50 for detailed drawings. Your local planning authority's validation checklist will specify exactly which scales are required for each drawing type.

A PNG image has no intrinsic physical size — it will print at whatever size your printer decides. To guarantee a specific scale, you need to embed your drawing in a PDF at the correct physical dimensions. Our tutorial explains how to do this for free using Google Docs: place your PNG at the correct size (e.g. 20cm × 10cm for a 20m × 10m drawing at 1:100), then download as PDF.

SimpleDraw is a free, browser-based floor plan and site plan drawing tool. You can draw walls, doors, windows, rooms, and outdoor features, and view your plans in 3D. It's designed for homeowners, DIY planners, and small-scale contractors. The basic drawing and export tools are free.