Scale Converter & Scale Calculator Online
Scale converter for maps, plans, and models. Scale calculation and conversion with ratios 1:10, 1:20, 1:50, 1:100, 1:200, 1:500.
Mode: calculating lengths from scale
Result
The scale determines the ratio between the length on a map or model and the actual length. A scale of 1:20 means that each unit on the map corresponds to 20 units in reality.
For example, if a segment 2.5 meters long on the map corresponds to 50 meters in reality, then the map’s scale is 1:20 (or 0.05 as a scale factor).
Scale Ruler
See what the selected scale looks like in practice — from map dimensions to real-world distances. Calibrate your screen for accurate readings.
The scale calculator converts real dimensions into lengths on a map, plan or model, and back again. If you know two lengths, it also works out the scale between them. It is built for architects, engineers, cartographers and model makers, and it works just as well for anyone who needs to read a drawing or build something to scale.
Say a distance of 50 meters measures 2.5 meters on the drawing. Enter both values and the calculator gives you a scale of 1:20. If you already know the scale, pick it from the common scales (1:10, 1:100, 1:25000 and others) and enter one length. The other appears right away.
Scale converter for architects and designers
How the scale calculator works
The calculator works in both directions. With a known scale, it turns a real length into a scaled length, or a scaled length into its real size. With two known lengths, it finds the scale. The note under the scale field tells you which mode is on.
Calculate a length from a scale
Enter the scale in the Scale Ratio field, for example 1:100, or click one of the common scales. Then type the real length, and the length on the map or plan appears straight away. It also works the other way round: enter a length you measured on the drawing to get the real size. At 1:100, 3.5 cm on a plan is 3.5 m in reality.
Find the scale from two lengths
Click the open lock () next to the scale. The lock closes (), the scale fields turn grey, and the calculator now works out the ratio from the two lengths as you type. With a real length of 50 m and a map length of 2.5 m, the result is 1:20.
In this mode a "Use an approximation" switch appears. It is on by default and rounds the ratio to a whole number. Turn it off if you need the exact value. To keep working with the scale you just found, click the lock again. The scale fields become editable, the calculated ratio stays in place, and every new length you enter is converted with it.
Measurement units
Each length has its own unit menu, so you can enter the real length in meters and the scaled length in centimeters. You can choose from:
- Metric: millimeters [mm], centimeters [cm], meters [m], kilometers [km]
- Imperial: inches [in], feet [ft], yards [yd], miles [mi]
- Nautical: nautical miles [nmi]
The lock next to each length field controls what happens when you switch units. By default the number is converted and the length stays the same, so 2.5 m becomes 250 cm. After you click the lock, the number stays as it is and the calculator recalculates the other length instead.
Scales for models, buildings and maps
The buttons on this page group common scales by use: 1:1 to 1:87 for models, 1:20 to 1:500 for architecture, and 1:25000 to 1:500000 for maps. You can also type any other ratio, such as 1:1000 or 1:20000.
You will find worked examples on the examples page. The calculator runs in your browser on computers, phones and tablets.
If you would rather measure straight off the drawing than type numbers, open our scale ruler: a graduated rule matched to the real size of your screen.
Frequently asked questions
Enter the scale, for example 1:10, and one of the two lengths: the real length or the length on the map or plan. The calculator fills in the other one. To find the scale instead, click the lock next to the scale field and enter both lengths.
Metric units (mm, cm, m, km), imperial units (in, ft, yd, mi) and nautical miles (nmi). Each length field has its own unit menu, so you can enter the real length in meters and the scaled length in centimeters.
The lock next to the scale switches modes. When it is open, the calculator works out lengths from the scale. When it is closed, it works out the scale from two lengths. The lock next to a length field decides what happens when you change the unit: either the number is converted and the length stays the same, or the number stays and the other length is recalculated.
Yes. Click the open lock next to the scale field, then enter the real length and the scaled length. For 50 m and 2.5 m the result is 1:20. The ratio is rounded to a whole number while the "Use an approximation" switch is on.
Any scale you type in, including 1:1, 1:10, 1:20, 1:100, 1:1000 and 1:20000. The buttons on the page give you quick access to common scales for models, architecture and maps.
Yes. It uses standard conversion factors and shows results to up to 8 decimal places, which is enough for architecture, engineering, cartography and technical drawing.