Model Building Calculator

miniThrottle: A model railroad WiFi throttle.

Instructions

This page contains calculations useful in building model machines and buildings. These include scale conversions, speed, distance, wheel diameter and gearbox ratios. Most scales below come from model railway building, but may also be useful for aircraft, cars and ships.

Calculations below include:

Optional settings: Custom scale and decimal place accuracy
Distance / Speed Conversion: using either Miles or kilometers
Decimal feet: convert feet and inches to feet in decimal fractions and mm equivalent
Length Equivalents: Scale to the millimeter equivalent of the selected scale
Wheel, speed and gearbox sizing: wheel diameters, model speeds and gearbox ratio

While the intention is to keep conversions accurate, please double check your work. We bear no responsibilty for any errors or misuse of these conversions. As calculations are perfored using metric values, there may be some "rounding error" on Imperial values, eg you need to enter 22.507 miles (ie 3 decimal places) before the equivalent G scale value shows an actual mile representing this distance.

Optional Settings

Use this section to select the decimal points required for calculations. NB Inch fractions are calculated as follows:

0 decimal points: nearest 1/8 inch
1 decimal points: nearest 1/16 inch
2 decimal points: nearest 1/32 inch
3 decimal points: nearest 1/64 inch

Decimal points

Optionally define a custom scale if the scale you want is not shown.

custom scale, 1:

Press Enter/TAB after updating fields for change(s) to take effect.

Distance / Speed Conversion

Use this for conversions of larger distances or speeds, eg km/h or mph, or track length. Distances may be fractional, eg 16.09 km. Use either Miles or Kilometers for input.

Press Enter/TAB after updating fields for change(s) to take effect.

Parameters
Miles
Kilometers

Calculations
Scale	Meter Equiv	Imperial Equiv

Decimal Feet

Use to convert from feet, inches and fractions to feet in decimal. Note the result also updates the succeeding length calculation. However, if required for wheel diameters, you will need to update these manually. Note entry is only to nearest 1/16 inch. Smaller values are likely to be insignificant once scaled. Equivalent values for other fractions are shown in the lookup table below:

Press Enter/TAB after updating fields for change(s) to take effect.

Inch fractions
1/2 inch	1/4 inch	1/8 inch	1/16 inch	mm Equiv
			1/16	1.5875
		1/8	2/16	3.1750
			3/16	4.7625
	1/4	2/8	4/16	6.3500
			5/16	7.9375
		3/8	6/16	9.5250
			7/16	11.1125
1/2	2/4	4/8	8/16	12.7000
			9/16	14.2875
		5/8	10/16	15.8750
			11/16	17.4625
	3/4	6/8	12/16	19.0500
			13/16	20.6375
		7/8	14/16	22.2250
			15/16	23.8125

Parameters
Feet
Inches
1/16ths

Calculations
Feet	0.0
mm	0.0

Notes:

1 Inch = 25.4mm
1 Foot = 304.5mm
Decimal feet equivalent from above is automatically carried forward to the length calculation below.

Length Equivalents

Use this to calculate component lengths, eg wall length, vehicle width, etc.

Press Enter/TAB after updating fields for change(s) to take effect.

Parameters
mm

Calculations
Scale	mm Equiv	Imperial Equiv

Wheel, speed and gearbox sizing

Use to calculate gearbox ratios, based on speed and wheel diameter. Note default values are selected to demonstrate the relationship between values, rather than representing any prototype. Using a lower ratio (eg 1:40 when 1:50 is indicated) will result in a model with a scale max speed faster than the prototype.

Press Enter/TAB after updating fields for change(s) to take effect.

Parameters
Wheel Diameter (mm)		prototype
Max Speed (km/h)		prototype
Max Motor Speed (rpm)		model

Calculations
Speed (meters/minute)		prototype
Speed (meters/second)		prototype
Distance per revolution (mm)		prototype (Circumference)
Max wheel rpm		both
Total gearing required (1:n)		model

Wheel Diameter (mm)		Speed (mm/s)	Imp. Diameter	Speed/sec

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