How do I calculate a 1:50 scale?

A scale of 1:50 is one divided by fifty, a factor of 0.02, so every model length is 0.02 times the real one. An actual 10 m at 1:50 is 20 cm on the model, which the page works as 10 m x 0.02 = 0.2 m, then 0.2 m converted into the unit you chose for the model. Set Work out to Model size, type the ratio, type the length you measured, and pick the unit for each side.

How do I find the real size from a model measurement?

Set Work out to Actual size and give the page the scale and the model measurement. It divides instead of multiplying: a 20 cm model at 1:50 is 0.2 m divided by 0.02, which is 10 m in the real thing. The steps under the answer show the division, so you can check it rather than trust it.

How do I work out what scale a model is?

Set Work out to The scale and give both lengths. The page divides the model length by the actual length, with both sides converted to metres first, and writes the answer as a ratio: an actual 10 m beside a 20 cm model comes back as 1:50. A scale that is not a tidy one is left as it falls, so a 1.83 m person modelled at 12 cm reads 1:15.25 rather than being rounded to a nearby number.

Can the two sides use different units?

Yes, and that is the point of the two unit lists. Each side offers millimetres, centimetres, metres, kilometres, inches, feet, yards and miles, chosen separately. A 14.8 ft car at 1:24 is 7.4 in on the model, and a 3.7 km stretch of road on a 1:25,000 map is 14.8 cm. Conversions use the international definitions, where 1 in is 0.0254 m and 1 mi is 1,609.344 m exactly.

What happens with an odd scale like 1:87.1?

It is used exactly as written. HO is 1:87.1, and an actual 20 m at that scale comes back as 229.621125144 mm, not the answer you would get from rounding the ratio to 1:87 first. The same holds for a ratio that is not in 1:n form at all: 3:4 stays 3:4, a factor of 0.75.

Does it handle enlargements and percentages?

Both. A ratio with the larger number first enlarges, so 2:1 doubles an actual 30 mm into 60 mm on the model. A percentage is read as a scale as well, the way a photocopier or a print dialog states it: 150% is a factor of 1.5, which turns 10 cm into 15 cm, and 50% is the same as 1:2.

Why does a scale written as a single number get refused?

Because 50 on its own could mean 1:50 or 50:1, and those are opposite answers: one shrinks a length fifty times, the other grows it fifty times. Rather than guess, the page asks you to write the half you mean first. A single number below one is not ambiguous, so 0.02 is accepted and shown as 1:50.

Does the page keep my numbers?

The linear scale form remembers its last entries in this browser only, and the Start over button at the top of the page forgets them. Recipe and solar-system entries are not saved. Calculations run in your browser without an account or upload.

How do I convert an architectural or blueprint scale?

For a metric drawing marked 1:50 or 1:100, enter that ratio. For an imperial label of 1/4 inch = 1 foot, convert both sides to inches: 0.25:12 is 1:48. A 1/8 inch = 1 foot label is 1:96. Enter the numeric ratio rather than the printed label, choose Actual size to convert a drawing measurement, and select inches for Model unit and feet for Actual unit. At 1:48 a 3 in drawing length gives an actual 12 ft. This is length conversion, not building or structural advice.

Can I calculate a map scale and a scale factor?

Yes. Choose The scale to divide model or map distance by actual distance after unit conversion; the Factor cell shows that ratio as a decimal. To find a map distance at a known ratio, choose Model size. The existing 1:25,000 example turns 3.7 km into 14.8 cm. Use distances measured consistently along the map; this page does not determine a projection or correct map distortion.

How do dollhouse and model scales work?

Enter the ratio specified for your model, such as 1:12 for a dollhouse or 1:64 for a miniature, and choose the actual and model units separately. At 1:12, an actual 6 ft length becomes 6 in. HO and N labels can vary by standard or region, so enter the stated numeric ratio; the page does not choose it from the label.

Can I scale a recipe up or down?

Open Scale recipe amounts or a solar system model, then choose Recipe amounts. Enter the original and wanted servings and an amount, name and unit for every ingredient. For 4 servings changed to 6, 250 g flour becomes 375 g, 300 ml milk becomes 450 ml and 2 eggs become 3. Units stay as entered; the form does not change cooking time, temperature or ingredient behaviour.

Can I make a solar system scale model?

Open Scale recipe amounts or a solar system model, then choose Solar system model. Enter the model Earth diameter in mm. A table scales the Sun, all eight planets and their rounded mean distances from the Sun with one common linear factor. Planet diameters and mean orbital distances come from NASA’s dated fact sheet; they are approximate reference values rather than current orbital positions.

Scale Calculator

Enter a scale ratio and the length you know, then choose Model size or Actual size. To find the ratio, choose The scale and enter both lengths. Each side has its own unit, so you can measure the actual length in metres and read the model in centimetres. Ratios such as 1:87.1 stay as typed instead of snapping to a common scale.

Model length20 cmscale 1:50 · actual 10 m · factor 0.02

Scale: 1:50
Actual: 10 m
Model: 20 cm
Factor: 0.02

The scale and the size

Leave the page one quantity to find. Each side keeps its own unit, so a 1:50 building can be measured in metres and built in centimetres without a conversion in your head.

Work out

Scale ratioActual lengthActual unitModel unit

The scale and the real thing are known: this is the size to build or draw.

Scale 1:50 is 1 / 50 = 0.02, so the model is 0.02 times the actual.
10 m x 0.02 = 0.2 m on the model.
0.2 m / 0.01 = 20 cm.

Worked cases

Each one runs through the same function the fields above do.

1:50, actual 10 msolve the model
20 cm
2:1, actual 30 mmenlarging
60 mm
1:50, model 20 cmsolve the actual
10 m

Unit conversions use the international definitions: 1 in is 0.0254 m and 1 mi is 1,609.344 m exactly. The US survey foot is a slightly different foot and is not offered here.
Numbers are shown to at most 12 significant figures. A browser works in binary floating point, so a longer tail would be noise rather than precision.
A ratio says nothing about material. Kerf, shrinkage, wall thickness and the tolerance of your printer or kit are not in this number, and a cut piece will not match it to the last decimal.

Scale recipe amounts or a solar system model

Scale a collection

Recipe amounts

Multiply every supplied amount by wanted servings divided by original servings. Units stay as entered. These entries are not saved.

Original servings

Wanted servings

Ingredient 1

Amount 1

Unit 1

Ingredient 2

Amount 2

Unit 2

Ingredient 3

Amount 3

Unit 3

Servings multiplier: 1.5.

Flour: 375 g
Milk: 450 ml
Eggs: 3 eggs

Decimal amounts only: write 0.5 for one half. Results are rounded to eight significant digits; fractional eggs are left fractional. This scales quantities, without converting units or adjusting cooking time, temperature, pan shape or ingredient behaviour.

Accuracy. Supplied recipe amounts use proportional arithmetic, displayed to eight significant digits. Solar model values are approximate NASA reference measurements scaled by one common linear factor.

Accuracy. Exact arithmetic: model length is actual length times the scale ratio, with each side converted from the unit you picked for it. Any one of scale, actual and model can be the unknown. The ratio is used exactly as you wrote it and is never rounded to the nearest common modelling scale.

Common questions

How do I calculate a 1:50 scale?: A scale of 1:50 is one divided by fifty, a factor of 0.02, so every model length is 0.02 times the real one. An actual 10 m at 1:50 is 20 cm on the model, which the page works as 10 m x 0.02 = 0.2 m, then 0.2 m converted into the unit you chose for the model. Set Work out to Model size, type the ratio, type the length you measured, and pick the unit for each side.
How do I find the real size from a model measurement?: Set Work out to Actual size and give the page the scale and the model measurement. It divides instead of multiplying: a 20 cm model at 1:50 is 0.2 m divided by 0.02, which is 10 m in the real thing. The steps under the answer show the division, so you can check it rather than trust it.
How do I work out what scale a model is?: Set Work out to The scale and give both lengths. The page divides the model length by the actual length, with both sides converted to metres first, and writes the answer as a ratio: an actual 10 m beside a 20 cm model comes back as 1:50. A scale that is not a tidy one is left as it falls, so a 1.83 m person modelled at 12 cm reads 1:15.25 rather than being rounded to a nearby number.
Can the two sides use different units?: Yes, and that is the point of the two unit lists. Each side offers millimetres, centimetres, metres, kilometres, inches, feet, yards and miles, chosen separately. A 14.8 ft car at 1:24 is 7.4 in on the model, and a 3.7 km stretch of road on a 1:25,000 map is 14.8 cm. Conversions use the international definitions, where 1 in is 0.0254 m and 1 mi is 1,609.344 m exactly.
What happens with an odd scale like 1:87.1?: It is used exactly as written. HO is 1:87.1, and an actual 20 m at that scale comes back as 229.621125144 mm, not the answer you would get from rounding the ratio to 1:87 first. The same holds for a ratio that is not in 1:n form at all: 3:4 stays 3:4, a factor of 0.75.
Does it handle enlargements and percentages?: Both. A ratio with the larger number first enlarges, so 2:1 doubles an actual 30 mm into 60 mm on the model. A percentage is read as a scale as well, the way a photocopier or a print dialog states it: 150% is a factor of 1.5, which turns 10 cm into 15 cm, and 50% is the same as 1:2.
Why does a scale written as a single number get refused?: Because 50 on its own could mean 1:50 or 50:1, and those are opposite answers: one shrinks a length fifty times, the other grows it fifty times. Rather than guess, the page asks you to write the half you mean first. A single number below one is not ambiguous, so 0.02 is accepted and shown as 1:50.
Does the page keep my numbers?: The linear scale form remembers its last entries in this browser only, and the Start over button at the top of the page forgets them. Recipe and solar-system entries are not saved. Calculations run in your browser without an account or upload.
How do I convert an architectural or blueprint scale?: For a metric drawing marked 1:50 or 1:100, enter that ratio. For an imperial label of 1/4 inch = 1 foot, convert both sides to inches: 0.25:12 is 1:48. A 1/8 inch = 1 foot label is 1:96. Enter the numeric ratio rather than the printed label, choose Actual size to convert a drawing measurement, and select inches for Model unit and feet for Actual unit. At 1:48 a 3 in drawing length gives an actual 12 ft. This is length conversion, not building or structural advice.
Can I calculate a map scale and a scale factor?: Yes. Choose The scale to divide model or map distance by actual distance after unit conversion; the Factor cell shows that ratio as a decimal. To find a map distance at a known ratio, choose Model size. The existing 1:25,000 example turns 3.7 km into 14.8 cm. Use distances measured consistently along the map; this page does not determine a projection or correct map distortion.
How do dollhouse and model scales work?: Enter the ratio specified for your model, such as 1:12 for a dollhouse or 1:64 for a miniature, and choose the actual and model units separately. At 1:12, an actual 6 ft length becomes 6 in. HO and N labels can vary by standard or region, so enter the stated numeric ratio; the page does not choose it from the label.
Can I scale a recipe up or down?: Open Scale recipe amounts or a solar system model, then choose Recipe amounts. Enter the original and wanted servings and an amount, name and unit for every ingredient. For 4 servings changed to 6, 250 g flour becomes 375 g, 300 ml milk becomes 450 ml and 2 eggs become 3. Units stay as entered; the form does not change cooking time, temperature or ingredient behaviour.
Can I make a solar system scale model?: Open Scale recipe amounts or a solar system model, then choose Solar system model. Enter the model Earth diameter in mm. A table scales the Sun, all eight planets and their rounded mean distances from the Sun with one common linear factor. Planet diameters and mean orbital distances come from NASA’s dated fact sheet; they are approximate reference values rather than current orbital positions.

Exact arithmetic: model length is actual length times the scale ratio, with each side converted from the unit you picked for it. Any one of scale, actual and model can be the unknown. The ratio is used exactly as you wrote it and is never rounded to the nearest common modelling scale.