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Load Cell vs Pressure Sensor: When to Weigh and When to Measure Pressure
A load cell measures force or weight directly, while a pressure sensor or gauge measures the pressure of a fluid or gas. They can often answer the same question, such as “how much liquid is in this tank?” or “how hard is this cylinder pushing?”, but they get there in different ways, and each fails in different situations. Use a load cell when you want the true mass or force, including solids, sticky products and pressurised vessels. Use a pressure sensor when you want the pressure itself, or a simple, low-cost indication of liquid level in a vented tank. This guide compares the two with worked examples so you can choose with confidence.
What each device measures
| Load cell | Pressure gauge or sensor | |
|---|---|---|
| Measures | Force, which is turned into weight or mass | Pressure, which is force per unit area |
| Where it sits | Under, over or in line with the load | In contact with the fluid or gas |
| Contact with the product | None. It is outside the vessel | Wetted by the product |
| Typical output | mV/V signal that needs conditioning | Dial, display, 4 to 20 mA or 0 to 10 V |
| Typical uses | Scales, hoppers, tank contents, force testing | Hydraulics, air, water, gas, process lines |
To learn more about each device first, read what is a load cell and pressure gauge vs pressure transmitter vs manometer.
The connection between pressure and force
Pressure and force are linked by area: force = pressure × area. That is why a pressure reading can sometimes stand in for a force or a weight, and why the two devices overlap.
- One bar equals 100,000 pascals (newtons per square metre).
- Water at the bottom of a 1 metre column exerts roughly 9.81 kPa, which is about 0.098 bar.
Those two facts power both examples below.
Example 1: how much liquid is in the tank?
A tank is 1.5 metres in diameter, with vertical walls, open to the air and filled to a depth of 2.5 metres with water.
- Floor area: π × 0.75 × 0.75 = about 1.767 square metres.
- Volume: 1.767 × 2.5 = about 4.42 cubic metres, so about 4,420 litres of water, or about 4,420 kg.
Using a pressure sensor at the bottom
Pressure at the bottom is density × gravity × depth: 1,000 × 9.81 × 2.5 = 24,525 pascals, or about 24.5 kPa. A pressure transmitter reads this and the controller converts it to a level or a volume.
Catch: the conversion assumes a density. If the liquid is 10% denser, say a brine at 1,100 kg per cubic metre, the pressure rises to about 26.98 kPa at the same depth. A system set up for water would show a level of about 2.75 metres, which is wrong by 10%. However, if the tank wall is vertical and you convert pressure to mass using the floor area (mass = pressure × area ÷ gravity), you get about 4,860 kg, which is correct for the denser liquid. So a pressure sensor can give a good mass reading in a vertical-walled, vented tank, but only if the control system is set up that way.
Using load cells under the tank
Load cells under the legs measure the actual weight of tank plus contents. After zeroing for the empty tank, they show the mass of the contents directly: about 4,420 kg for water, or about 4,860 kg for the denser brine, with no need to know the density. They also work if the tank is pressurised, has a conical bottom, or the product forms deposits.
Comparison for this tank
| Factor | Pressure sensor | Load cells |
|---|---|---|
| Cost | Low: one sensor | Higher: three or four cells and a junction box |
| Installation | Fit to a tank port; no need to lift the tank | Tank must sit on the cells; piping must be flexible |
| Contact with product | Wetted, so it needs to suit the media and cleaning | None |
| Density changes | Affects level and volume readings | Not an issue for mass |
| Solids and sticky products | Poor. Powders have no hydrostatic head | Good |
| Pressurised tanks | Needs a second sensor for headspace pressure | Unaffected |
| Wind, pipes and mounting | Not affected | Affected; careful design needed |
| Accuracy | Good for level in simple tanks | Good for mass, even in difficult tanks |
For the mechanics of weighing vessels, see tank, silo and hopper weighing with load cells.
Example 2: how hard is the hydraulic cylinder pushing?
A press uses a hydraulic cylinder with a 50 mm bore, and the gauge reads 100 bar.
- Piston area: π × 0.025 × 0.025 = about 0.001963 square metres.
- Pressure: 100 bar = 10,000,000 pascals.
- Force: 10,000,000 × 0.001963 = about 19,635 newtons, which is about 2,000 kilograms-force.
That is the theoretical force. In the real world, seal friction, back pressure on the rod side and temperature reduce the force actually delivered. If you only need to know the press is working, the gauge is enough. If you need to record the true force applied to a part, put a load cell in line with the cylinder. A tension and compression cell such as the Revere 9363 reads the real force.
| Question | Pressure gauge | Load cell |
|---|---|---|
| Is the press developing pressure? | Yes, ideal | Not needed |
| What is the true force on the part? | Estimate only | Measured directly |
| Is the relief valve opening at the right pressure? | Yes, ideal | Not applicable |
| Test and quality record of force | Weak evidence | Strong evidence |
For testing hydraulic pressure, see digital hydraulic pressure gauges.
Which to use? A practical guide
| Situation | Better choice | Why |
|---|---|---|
| Vented water tank, level indication only | Pressure sensor | Simple, low cost |
| Tank of varying product, charged by weight | Load cells | Mass independent of density |
| Powder or grain silo | Load cells | No hydrostatic head in solids |
| Pressurised reactor | Load cells, or differential pressure plus density correction | Headspace pressure complicates the reading |
| Checking pump or compressor pressure | Pressure gauge | That is what the gauge measures |
| Press force or material testing | Load cell | Measures the actual force |
| Hanging or crane weighing | Load cell | The only practical choice |
| Remote monitoring of line pressure | Pressure transmitter | Sends a signal to a control system |
Examples from our range
- Pressure sensor: the WIKA Model A-10 offers 4 to 20 mA and 0 to 10 V outputs, with gauge, absolute and compound versions and 316L stainless steel wetted parts. See Pressure Sensor SNG-A10.
- Digital pressure gauges: the PDK PDR range reads pressure to 0.025% to 0.5% of full scale. See the digital pressure gauge buying guide.
- Tank load cells: the Sensortronics 65016-W is a stainless steel shear beam designed for tank, bin and silo weighing.
- Hanging hopper cells: the Sensortronics 60063 S-type suits suspended vessels.
Can I use both?
Yes, and many good systems do. A pressure sensor on a tank gives a quick, low-cost level signal for pump control, while load cells provide the accurate mass for batching and stock records. Comparing the two readings can also reveal problems such as a blocked sensor, build-up inside the tank or a binding load cell mount.
Accuracy and quality: what to compare
- For pressure sensors: accuracy as a percentage of full scale, temperature effect, wetted material, output type and long-term stability. See pressure gauge accuracy compared in real numbers.
- For load cells: total error, class (such as C3 or C6), IP rating, material and certification. See load cell accuracy and quality compared.
- For both: calibration traceability and supplier support. See the supplier checklist.
Common mistakes
- Using a pressure sensor on a powder. Solids do not create a fluid head, so the reading is meaningless.
- Forgetting headspace pressure. In a closed tank, the pressure above the liquid adds to the reading and must be removed or measured.
- Fixing pipes to a weighed tank. Stiff pipework carries part of the load and ruins a load cell reading.
- Assuming a clean sensor. Build-up on a pressure sensor diaphragm changes the reading over time.
- Treating cylinder pressure as exact force. Friction and back pressure reduce the real force.
Cost and complexity at a glance
A pressure transmitter is usually a single, low-cost device that fits to an existing port. A weighing system uses several load cells, mounting hardware, a junction box and an indicator, so it costs more to buy and install, and needs more careful design. In return it measures the true mass and does not touch the product. Weigh the extra cost against the cost of a wrong reading, and the answer is usually clear.
Frequently asked questions
Can a pressure sensor weigh a tank?
In a vented tank with vertical walls, pressure at the bottom is proportional to the mass above it, so with the right set-up it can. It does not work for powders, pressurised tanks or sticky products.
Which is cheaper to install?
A pressure sensor, in most cases. Load cells need the vessel to be supported on them and piped flexibly.
Which is more accurate?
It depends on the application. For mass in difficult conditions, load cells. For simple level in a clean liquid tank, a good pressure sensor can be more than adequate.
Do I need a pressure sensor if I have load cells?
Not for weight. You might still want pressure sensors on lines and pumps.
What do I use for a hydraulic press?
A pressure gauge or transmitter for pressure, and a load cell if you need the true force.
Next steps
Start with our complete load cell guide or the gauge, transmitter and manometer comparison, then contact us with your application and we will recommend the better approach, even if that means a simpler device.
