how accurate are the sensors and propane sensor for levels

Maybe the filling was measured in pounds rather than gallons. 30 pounds is somewhere in the vicinity of 7.5 to 8 gallons.

Ok I can see the needle around the sensor, it was a little over 1/2 full...lights said 2/3
I had it filled it took just under 5 gallons...now the needle is on full and the lights say full
I cant believe the propane is only 18 gallons, the guy filling it said 30

THe old saying is the least accurate gauge made is a fuel gauge..

Seriously on Propane the "It reads full till it's empty" applies to inline pressure gauges used for luggable tanks. If you have a motor home you have a float type gauge and the dial on the outside is very accurate. Well. Very "repeatable" let's put it that way.. you may have more, or less than you think but when it says for example Half full.. Well you have x gallons. and the next time it says half full you have exactly x gallons, not one pint more or less.

The Fridge SIPS gas. and I mean SIPS .. Not like the stove which eats the gas or the Water heater or furnace with GOBBLE IT IN MASSIVE AMOUNTS.. The Fridge just sips.

How big is your propane tank....gallons?
What fridge brand/model?

Gallon of propane has 91,500btu
A very large RV fridge has a 2200btu/hr burner
Furnace....20,000 --42,000btu/hr
Water heater....10,000-12,000btu/hr
Stove top burners.....5,000--9,000 btu/hr
Oven......1200--1500btu/hr

Look up your RV propane appliance btu/hr ratings....add them up
That is how much propane would be burned if ALL where in operation for a FULL Hour

Do some research on your items so you can get an idea on requirements
THen over time you will see just how much is used/needed for YOUR usage



Just a quick check a 2013 Vista 26 has an 18 gal capacity tank
80% is 14.4 gal

My RV has a built in lp tank with gauge. When it goes from 1/4 to E, it is half full.

I don’t even bother with the other gauges.

It sounds as though you do have a permanent built-in tank with the usual sender mounted on the dial gauge. You should be able to see the pointer on the gauge despite the sender being on top of it if you look closely enough.

The three light gauges (often they do have four lights, but the bottom light is always on so there are only three that do anything) are accurate for propane but not at all precise. In other words, the points where it changes from full to 2/3 to 1/3 to empty are pretty repeatable and usually reasonably calibrated, but there's a lot of room between each step. The readings for the black tank, on the other hand, are often both inaccurate and imprecise.

The fridge uses not much propane at all, maybe a pound a day as a very rough rule of thumb (and probably a bit less than that). A year ago I took an extended trip to Alaska, 2 and a half months, and went through about two tanks of propane (with a built-in tank, not cylinders) for the entire trip.

Fill both of your tanks...hopefully you have two. When one runs out switch to the other tank, drive into town and fill the empty one. As said fridges are not a big user of propane.

If you're using bottles, get one of these. Uses sound to detect the difference in density of the liquid and gas. Any of those stick-on detectors require a temp difference and you only get that when the gas is flowing.

If you have a large built-in tank, the level gauge is probably a float type and should be accurate to within a 1/4 tank. Remember that a full propane tank reads 3/4.

I can go a whole season on one tank of propane if I don't use the furnace. Cooking does not use much, but we don't use the oven at all. When they fill the propane, they don't fill to 100%, there's a safety factor built in.

One problem with those "Empty,1/3,2/3,Full" sensor systems is that you don't know if the level is actually 2/3, or is it just barely below the full sensor. Is it really "Empty" or is it just a tick below the 1/3 sensor. There are more accurate sensor systems that read out in percentages using external sensors that don't gum up, but few RV manufacturers install them since they cost a few dollars more.