# Calculators

## 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

## Capacitor energy from capacitance and voltage 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.

C

V

#### Formula

$$E = \frac{1}{2}\cdot{}C\cdot{}U_p^2$$

#### Python code

You can use the UliEngineering library like this:

from UliEngineering.Electronics.Capacitors import capacitor_energy
from UliEngineering.EngineerIO import auto_format, auto_print

# These are equivalent:
energy = capacitor_energy("100 uF", "24 V") # energy = 0.0288 (J)
energy = capacitor_energy(100e-6, 24.0) # energy = 0.0288 (J)

# ... or get out a human-readable value:
energy_str = auto_format(capacitor_energy, "100 uF", "24 V") # "28.8 mJ"
# ... or print directly
auto_print(capacitor_energy, "100 uF", "24 V") # prints "28.8 mJ"


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

def capacitor_energy(capacitance, voltage):
return 0.5*capacitance*voltage*voltage

# Usage example:
print(capacitor_energy(100e-6, 24.0)) # prints 0.0288 (J)

Posted by Uli Köhler in Calculators, Electronics

## X1/X2/Y1/Y2/Y4 impulse withstand rating voltage calculator (IEC 60384-14)

IEC 60384-14 specifies that X1/X2-rated capacitors shall be tested to withstand an impulse voltage of 4 kV (X1), 2.5 kV (X2, Y4), 8 kV (Y1) or 5 kV (Y2).

However these values only apply for a capacitance $\leq 1 μF$ (except for Y1/Y4 capacitors). Use this calculator for X1/X2/Y2 capacitances $> 1 μF$!

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.

F

#### Formula:

$$Up = \frac{Up_{\leq 1 μF}}{\Large\sqrt{\frac{C}{1\,000\,000\frac{μF}{F}}}}$$

where:

• $Up$ is the impulse withstand voltage rating
• $C$ is the capacitance in Farads
• $Up_{\leq 1 μF}$ is the voltage rating for that capacitor class with a capacitance of $\leq 1 μF$:
• For X1-class: 4 kV
• For X2-class: 2.5 kV
• Y1-class impulse withstand voltage is always 8 kV no matter what capacitance
• For Y2-class: 5 kV
• Y4-class impulse withstand voltage is always 2.5 kV no matter what capacitance

#### Why is the impulse withstand voltage lower for larger capacitors?

The rationale behind the derating of the impulse withstand voltage is that larger capacitances will have sufficient capacitance so that a given overvoltage doesn’t cause a large voltage spike in the capacitor.

The formula (see above) is chosen so that the energy in the capacitor:

$$E = \frac{1}{2}\cdot{}C\cdot{}U_p^2$$

is kept constant (i.e. at the same value as for a equivalent capacitor of 1 μF).

Posted by Uli Köhler in Calculators, Compliance, Electronics

## Inductive reactance online calculator & Python code

Use this online calculator to compute the reactance of an inductor in Ω at a specific frequency given its inductance.

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.

H

Hz

#### Formula:

$$X_L = 2\pi fL$$

#### Python code:

The preferred way is to use UliEngineering’s UliEngineering.Electronics.Reactance.inductive_reactance:

from UliEngineering.Electronics.Reactance import *
# You can either pass strings like "150 uH" or values like 150e-6

inductive_reactance("150 uH", "10 MHz") # returns 9424.77796076938

from UliEngineering.Electronics.Reactance import *
from UliEngineering.EngineerIO import *

# Compute value as a string
xc = auto_format(inductive_reactance, "150 uH", "10 MHz") # "9.42 kΩ"

# ... or print directly
auto_print(inductive_reactance, "150 uH", "10 MHz") # prints "9.42 kΩ"

In case you can’t use UliEngineering and you want to do it manually, here’s a minimal example:

import math
def inductive_reactance(f, l):
"""Compute the inductive reactance"""
return 2*math.pi*f*l
Posted by Uli Köhler in Calculators, Electronics, Python

## Capacitive reactance online calculator & Python code

Use this online calculator to compute the reactance of a capacitor in Ω at a specific frequency given its capacitance.

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.

F

Hz

#### Formula:

$$X_C = \frac{1}{2\pi fC}$$

#### Python code:

The preferred way is to use UliEngineering’s UliEngineering.Electronics.Reactance.capacitive_reactance:

from UliEngineering.Electronics.Reactance import *
# You can either pass strings like "150 pF" or values like 150e-12

capacitive_reactance("150 pF", "10 MHz") # returns 106.1032953945969

from UliEngineering.Electronics.Reactance import *
from UliEngineering.EngineerIO import *

# Compute value as a string
xc = auto_format(capacitive_reactance, "150 pF", "10 MHz") # "106 Ω"

# ... or print directly
auto_print(capacitive_reactance, "150 pF", "10 MHz") # prints "106 Ω"

In case you can’t use UliEngineering and you want to do it manually, here’s a minimal example:

import math
def capacitive_reactance(f, c):
"""Compute the capacitive reactance"""
return 1./(2*math.pi*f*c)
Posted by Uli Köhler in Calculators, Electronics, Python

## Volts to dBµV online calculator & Python code

Use this online calculator to convert a voltage in Volts to a voltage in dBµV.

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

#### Formula:

$$U_{\text{dBµV}} = \frac{20\cdot\log(1\,000\,000 \cdot U_V)}{ \log(2) + \log(5)}$$

#### Python code:

import math
def volts_to_dbuv(v):
"""Convert a voltage in volts to a voltage in dBµV"""
return (20*math.log(1e6 * v))/(math.log(2) + math.log(5))

Posted by Uli Köhler in Calculators, Electronics