Every resistance-based level sender works by changing its resistance as the float moves up and down. That resistance is read and turned into a needle position on the gauge. There are two standards for how much resistance means full and how much means empty — European and American — and the only thing that really matters is that your sender and gauge speak the same one.
The short version
European runs 0 ohms empty to 190 ohms full. American runs 240 ohms empty to 30 ohms full. Pair a sender and gauge of different standards and the gauge reads backwards — full when the tank is empty, empty when it's full.
01The two standards
Both do exactly the same job; they just use opposite ends of the resistance range for full and empty.
European
0 ohms empty → 190 ohms full
Resistance rises as the tank fills. The most common standard on European-built boats and vehicles.
American
240 ohms empty → 30 ohms full
Resistance falls as the tank fills. Historically favoured by US boat builders.
These two standards cover roughly 90% of all standard senders. Car and commercial-vehicle manufacturers often run their own resistance range on factory-fit systems, but in the marine market European and American account for around 99% of senders.
The names are historical, not technical — much like 240 V / 110 V mains or the old PAL / NTSC video standards. Today both resistance ranges are used on both sides of the Atlantic, and there is no advantage or disadvantage to either. The only wrong choice is mixing them.
02Why the resistance matters
- The sender and gauge must share the same standard. A European sender needs a European gauge; an American sender needs an American gauge.
- Mix them and the gauge reads backwards — this is the single most common cause of a "brand new sender reading wrong". It isn't faulty; it's the wrong standard.
- If you're converting an analogue sender to a digital network such as NMEA 2000, you need to know the sender's resistance standard to choose and set up the right converter correctly.
03Which standard is my sender?
The quickest check is at the sender. Set a multimeter to resistance (Ω) and take a reading with the float at the top (full) and again at the bottom (empty) — the two figures tell you the standard. Full step-by-step on how to test a sender.
European sender
190 ohms full · 0 ohms empty
±10 ohms at each end.
American sender
30 ohms full · 240 ohms empty
±10 ohms at each end.
04Which standard is my gauge?
No sender to hand? You can read the standard off the gauge instead. Disconnect the sender feed and compare the needle with that terminal left open against touching it to battery negative. Full step-by-step on how to test a gauge.
European gauge
Disconnected → FULL · battery negative → EMPTY
Open circuit reads full; 0 ohms (battery negative) reads empty.
American gauge
Disconnected → EMPTY · battery negative → FULL
Open circuit reads empty; 0 ohms (battery negative) reads full.
Need a replacement?
Match the standard, match the reading
If you're replacing a sender or gauge, order the same resistance standard as the part it pairs with. Not sure what you've got? The two test pages walk you through it.
05Common questions
Can I use a European sender with an American gauge?
No. They'd be on opposite resistance standards, so the gauge would read backwards. Either match the sender to the gauge's standard or replace the gauge to match the sender.
My new sender reads backwards — is it faulty?
Almost certainly not. A backwards reading is the classic sign of a resistance mismatch — a European part paired with an American one, or vice versa. Check the standard of both the sender and the gauge before assuming anything is broken.
How do I know which standard my boat or vehicle uses?
Test whichever part you still have — gauge or sender — using the checks above. The reading tells you the standard, and you then match the replacement to it. There's no way to tell by looking; you have to measure.
Does the standard matter when converting to NMEA 2000?
Yes. The converter needs to know the sender's resistance standard to scale the reading correctly, so identify it first using the multimeter check above.
Still unsure which standard you have? Read how to test a sender and how to test a gauge, or get in touch with your readings and we'll point you to the right part.
