# Calculators

## FR4 PCB thermal expansion online calculator

Calculate the thermal expansion in millimeters (mm) of a FR4 PCB in X/Y direction. A typical temperature difference default is 65°C, the difference between 20°C room temperature and the max temperature rating of 85°C parts. The default 13ppm/°C thermal expansion coefficient is from this website.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

mm

°C

ppm/°C

Posted by Uli Köhler in Calculators, Electronics, Physics

## Resistor temperature coefficient calculator

Calculate the minimum and maximum value of a resistor based on its temperature coefficient.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

Ω

ppm

°C

°C

Posted by Uli Köhler in Calculators, Electronics

## Sense resistor power dissipation calculator

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

Too much power dissipation? You need to use a current sense amplifier ! See our Sense resistor / current shunt + current sense amplifier calculator !

Want to calculate the correct sense resistor value for your desired sense voltage? See Sense resistor / current shunt calculator

This calculator allows you to find out how much power your sense resistor will dissipate and how much voltage it will drop at a given current.

A

Ω

$$R_{text{sense}} = frac{U_{text{drop}}}{I_{text{sense}}}$$ $$P_{text{sense}} = I_{text{sense}}² cdot R_{text{sense}}$$
Posted by Uli Köhler in Calculators, Electronics

## RTC battery lifetime online calculator

Free calculator to estimate how long your battery (e.g. CR2032) will last in your microcontroller RTC application. Note: The default capacity of 220 mAh is a typical capacity for a CR2032 coin cells.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

Ah

A

Posted by Uli Köhler in Calculators, Electronics

## How long does a I²C message transmission take? Online calculator

Enter the number of data bytes to be transmitted (excluding the start byte containing the slave address & RW bit).

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

bytes

$$N_{\text{bits}} = (N_{\text{bytes}} + 1) \cdot 9$$$$\Delta T_{\text{transmission}} = N_{\text{bits}} / \text{bitrate}$$

Posted by Uli Köhler in Calculators, Electronics

## Pressure in a rotating body of liquid calculator

This online calculator allows you to calculate the pressure of a rotating body of liquid with a given density at a specified radius. Note that gravity is not accounted for and the pressure is relative to the pressure at r=0. See this forum post for more details on the formula.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

kg/m³

Hz

m

$$\omega = 2\cdot\pi\cdot n[Hz]$$
$$P = \frac{1}{2}\cdot\rho\cdot\omega²\cdot r²$$

Posted by Uli Köhler in Calculators

## Hollow cylinder volume calculator (from diameters & height)

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

m

m

m

$$V = \pi\cdot(\frac{OD}{2})²\cdot h\ -\ \pi\cdot(\frac{ID}{2})²\cdot h$$

Posted by Uli Köhler in Calculators

## Centrifuge acceleration calculator (from rpm and diameter)

Calculate the acceleration from its rotational speed in RPM and its diameter using this online calculator – formula included.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

rpm

m

$$n[rps] = \frac{n[rpm]}{60\frac{s}{min}}$$$$a[m/s²] = 4\cdot\pi^2\cdot(\frac{d}{2})\cdot(n[rps])²$$$$a[g] = \frac{a[m/s²]}{9.80665\frac{m/s²}{g}}$$

Posted by Uli Köhler in Calculators

## Centrifuge diameter calculator (from acceleration & rpm)

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

rpm

g

$$a[m/s²] = a[g] \cdot 9.80665\frac{m/s²}{g}$$$$n[rps] = \frac{n[rpm]}{60\frac{s}{min}}$$$$d_{centrifuge} = 2\cdot\frac{a[m/s²]}{4\cdot\pi^2\cdot(n[rps])²}$$

Posted by Uli Köhler in Calculators

## Tube volume calculator

Calculate the volume of a tube by its length and diameter using this online calculator – formula included.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

m

m

Posted by Uli Köhler in Calculators, Hardware

## Lehman scale fee calculator

Calculate broker fees using the origin Lehman scale, double Lehman scale and modern Lehman scale using this online calculator.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

\$

Posted by Uli Köhler in Calculators, Economics

## FFT spectrum frequency resolution calculator

Calculate the frequency resolution of a FFT spectrum using this online calculator – formula included.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

points

Hz

$$f_{resolution} = \frac{f_{samplerate}}{N_{FFT}}$$

Posted by Uli Köhler in Calculators, Data science

## Hz to RPM converter

Convert rotational speed from Hz to RPM using this online calculator – formula included.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

Hz

$$f_{RPM} = f_{Hz} \cdot 60$$

Posted by Uli Köhler in Calculators

## RPM to Hz converter

Convert rotational speed in Hz to RPM using this online calculator – formula included.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

RPM

$$f_{Hz} = \frac{f_{RPM}}{60}$$

Posted by Uli Köhler in Calculators

## Simple body surface area calculator

Calculate the body surface area using the Mosteller, DuBois, Haycock, Gehan & George and Boyd formulas using this online calculator.

This information is presented for informational purposes only and is intended for professionals. While we strive to provide accurate information, this information might be outdated, unintentionally misleading or incorrect. Consult a medical professional and/or read the primary sources cited in our article before basing any decision on this information.
TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

m

kg

Sources & Formulae: Halls.md

Posted by Uli Köhler in Calculators

## Grams-to-mol online converter

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

g

g/mol

$$n[mol] = \frac{m[g]}{M_m[\frac{g}{mol}]}$$
Posted by Uli Köhler in Calculators

## Incandescent bulb power calculator

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

V

A

$$P_{\text{bulb}} = U_{\text{bulb}} \cdot I_{\text{bulb}}$$
Posted by Uli Köhler in Calculators, Electronics

## Relay coil current calculator (from coil power and voltage)

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

V

W

$$I_{\text{coil}} = \frac{P_{\text{coil}}}{U_{\text{coil}}}$$
Posted by Uli Köhler in Calculators, Electronics

## Voltage divider output voltage calculator (from R1 & R2)

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

Input voltage:

V

Top resistor:

Ω

Bottom resistor:

Ω

$$V_{out} = V_{in} \cdot \frac{R_2}{R_1\cdot R_2}$$
Posted by Uli Köhler in Calculators, Electronics

## Lumen to Candela online calculator & Python code

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

lm

°

#### Formula

$$\Omega_{sr} = 2\cdot\pi\cdot(1-\cos(\frac{\theta}{2}))$$
$$I_{v} = \frac{\Phi_v}{\Omega_{sr}}$$

where:

• $\theta$ is the apex angle in radians
• $\Omega_{sr}$ is the solid angle in Steradians
• $\Phi_v$ is the luminous flux in lux (lx).
• $I_{v}$ is the luminous intensity in candela (cd).

#### Python code

You can use the UliEngineering library like this:

from UliEngineering.Physics.Light import lumen_to_candela_by_apex_angle
from UliEngineering.EngineerIO import auto_format, auto_print

# These are equivalent:
intensity = lumen_to_candela_by_apex_angle("25 lm", "120°") # intensity = 7.9577 (cd)
intensity = lumen_to_candela_by_apex_angle(25.0, 120.0) # intensity = 7.9577 (cd)

# ... or get out a human-readable value:
intensity_str = auto_format(lumen_to_candela_by_apex_angle, "25 lm", "120°") # "7.96 cd"
# ... or print directly
auto_print(lumen_to_candela_by_apex_angle, "25 lm", "120°") # prints "7.96 cd"


In case you can’t use UliEngineering, use this Python function:

import math

def lumen_to_candela_by_apex_angle(flux, angle):
"""
Compute the luminous intensity from the luminous flux,
assuming that the flux of <flux> is distributed equally around
a cone with apex angle <angle>.

Keyword parameters
------------------
flux : value, engineer string or NumPy array
The luminous flux in Lux.
angle : value, engineer string or NumPy array
The apex angle of the emission cone, in degrees
For many LEDs, this is

>>> lumen_to_candela_by_apex_angle(25., 120.)
7.957747154594769
"""
solid_angle = 2*math.pi*(1.-math.cos((angle*math.pi/180.)/2.0))
return flux / solid_angle

# Usage example
print(lumen_to_candela_by_apex_angle(25., 120.)) # Prints 7.957747154594769 (cd)

Posted by Uli Köhler in Calculators, Physics