---
title: "Kidneys — what it does and the numbers"
description: "Two fist-sized filters processing about 180 litres of blood a day. What it does, where it is, the figures people look up, and the widely repeated claims that turn ou"
url: https://atoneplace.net/body/kidneys/
site: "At One Place"
---

# Kidneys

**Kidneys: Two fist-sized filters processing about 180 litres of blood a day.**

Filter blood, regulate fluid balance, control blood pressure and electrolytes, and produce hormones governing red blood cell production and calcium absorption. They filter around 180 litres of fluid a day and return almost all of it, producing 1 to 2 litres of urine.

## Where it is

Either side of the spine at the back, roughly at the level of the lowest ribs.

## The numbers

- **Mass each:** 120–170 g
- **Nephrons per kidney:** about 1 million
- **Fluid filtered daily:** ~180 litres
- **Urine produced:** 1–2 litres

## Worth knowing

Kidneys receive about 20% of the heart’s output despite being under half a per cent of body mass. The right kidney sits slightly lower than the left, pushed down by the liver above it.

> Structural reference only — this is not medical advice, and individual variation in every figure here is substantial. Anything concerning your own health belongs with a clinician rather than a reference page.

## Common questions

### What does the kidneys do?

Filter blood, regulate fluid balance, control blood pressure and electrolytes, and produce hormones governing red blood cell production and calcium absorption.

### Kidneys — key numbers

Mass each: 120–170 g. Nephrons per kidney: about 1 million. Fluid filtered daily: ~180 litres. Urine produced: 1–2 litres.

## Related pages

- [Heart](https://atoneplace.net/body/heart/)
- [Brain](https://atoneplace.net/body/brain/)
- [Liver](https://atoneplace.net/body/liver/)
- [Lungs](https://atoneplace.net/body/lungs/)
- [Skin](https://atoneplace.net/body/skin/)
- [Bones](https://atoneplace.net/body/bones/)
- [Blood types](https://atoneplace.net/body/blood-types/)
- [Teeth](https://atoneplace.net/body/teeth/)
- [Blood](https://atoneplace.net/body/blood/)
- [The senses](https://atoneplace.net/body/senses/)
- [Taste](https://atoneplace.net/body/taste/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)