# Differential Pressure Calculator (Kv)

URL: https://speedycalculator.com/calculators/physics/differential-pressure/
Last updated: 2026-10-30

> The differential pressure calculator finds the pressure drop across a valve or fitting from the flow rate, its Kv value and the liquid's specific gravity.

## Inputs

- Liquid
- Specific gravity
- Flow rate Q (m³/h, L/min, L/s, US gpm)
- Flow coefficient K_v (m³/h)

## Results

- Pressure drop ΔP

## Formula

```
ΔP (bar) = SG·(Q (m³/h) / K_v)²
```

## Explanation

Every valve has a Kv: the flow of water in m³/h that causes a 1 bar drop. Knowing it, you can predict the pressure drop at any flow – essential for balancing heating systems and sizing pumps.

### How to use the Differential Pressure Calculator

- **Liquid**
- **Specific gravity**
- **Flow rate Q**
- **Flow coefficient K_v (m³/h)**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the liquid, enter the flow rate and the valve's Kv.

### Inputs explained

FieldWhat to enterLiquidChoose one: Water, Seawater, Ethanol, Acetone …Specific gravityA numberFlow rate QUnits: m³/h, L/min, L/s, US gpmFlow coefficient K_v (m³/h)A number

### Example values

How the main result changes when **Specific gravity** changes and everything else stays at the example values above:

Specific gravityPressure drop ΔP (bar)0.50.250.750.2510.251.250.251.50.2520.25

## Worked example

Inputs — Liquid: Water; Flow rate Q: 2 m³/h; Flow coefficient K_v (m³/h): 4.

Results — **Pressure drop ΔP = 0.25 bar**.

## Key terms

- **Differential pressure**: Pressure difference between two points.

## FAQ

**What is Kv?**
The water flow in m³/h through a valve at 1 bar pressure drop.

**How does the drop scale with flow?**
With the square of the flow rate.

**How do Kv and Cv relate?**
Cv = 1.156·Kv.

**Why is SG included?**
Denser liquids produce a larger drop at the same flow.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)