What is the oddest/most obscure conversion factor you have memorized because it is handy in your line of work (and why)? Mine: 1 kilowatt-hour (kWh) = 3,412 British thermal units (Btus), because for some reason we Americans discuss fuel costs in $/million Btus & power plant heat rates in Btu/kWh.

1 jelly donut = 1 MJ = 250 kcal doi.org/10.1119/1.19...

AC three phase amps to kilowatts calculation formula P(kW) = √3 × PF × I(A) × VL-L(V) / 1000 Useful when someone knows how much spare switchboard capacity they have & they want to know what size DC EV charger they can install.

This is in imperial units. 1 cubic foot of natural gas, at 550psi, s.g. of 0.592 and 20c, Weighs 1.88525 lbs Used to be involved in high pressure gas metering.

I carry this one as well, in a slightly modified form. A US/NA plug in space heater is typically ~1.5 kW of output or roughly 5000 BTU/hr, which is a nice touch point for intuition about heat pump output given in the same units (for.... reasons).

The leak adjusted emissions factor for natural gas assuming a 20 year GWP of 86 is 21.3 (lbs. CO2e / therm) adjusted for molecular weight of CH4/CO2 and local pipeline leakage rate of 2.7% and EIA baseline natural gas emissions of 11.708 (lbs. CO2 / therm). 100,000 Btu / therm of natural gas.

The conversion factor from photon wavelength to photon energy is about 1240 eV • nm

that pi * 10^7 is a pretty good approximation for the number of seconds in a year

Another one still in use is water: 1 acre-foot = 1233 m^3

250g is 8oz + 10%. Because I worked in grocery sales.

Trunk circumference to Diameter at Breast Height (DBH). I don’t actually do the conversion very often because I have a tape measure to do it. It’s not very odd or obscure except in this application—just circle geometry (trees rarely being exactly circular, dividing C/pi gives an estimate of D).