Same idea, different water
Both coefficients answer "how much water flows through this valve at a reference pressure drop?" — they just pick different references:
Cv is US GPM of 60 °F water at 1 psi; Kv is m³/h of water at 1 bar. The 1.156 factor is just those unit systems colliding. Nothing about the valve changes — a Kv 41 valve and a Cv 47.4 valve are the same piece of hardware described in two languages.
Quick reference
| Kv | Cv | Kv | Cv |
|---|---|---|---|
| 1 | 1.16 | 40 | 46.2 |
| 2.5 | 2.89 | 63 | 72.8 |
| 6.3 | 7.28 | 100 | 115.6 |
| 10 | 11.56 | 160 | 185.0 |
| 16 | 18.5 | 250 | 289.0 |
| 25 | 28.9 | 400 | 462.4 |
(The Kv column deliberately follows the R10 preferred-number series European valve trims are actually offered in.)
Field notes
- Check which coefficient a datasheet means before comparing valves — a 13% mix-up is enough to land on the wrong trim size.
- Kvs vs Kv: European sheets often write Kvs for the coefficient at 100% travel, reserving Kv for the value at an operating point.
- Need the coefficient from process data instead? Use our liquid Cv sizing calculator.
Frequently asked questions
What is the conversion between Cv and Kv?
Cv = 1.156 × Kv, and Kv = 0.865 × Cv. The factor comes from the different reference conditions: Cv uses US GPM at 1 psi, Kv uses m³/h at 1 bar.
What is a Kv value?
Kv is the metric valve flow coefficient: the flow of water in m³/h that passes through the valve at a 1 bar pressure drop. European valve datasheets state Kv; American ones state Cv.
What is Av and how does it relate?
Av is the SI flow coefficient in m², used in IEC 60534: Av = 2.78×10⁻⁵ × Kv = 2.40×10⁻⁵ × Cv. It appears in formal sizing standards more than on datasheets.
Provided for reference and education. Verify independently before use in safety-critical work. See our disclaimer.