Hydraulic Orifice Calculator - SI units
Q=CA√(2ΔP/ρ), A=πd²/4, ρ=1000*SG; bar→Pa*1e5, mm→m/1000,
m³/s→L/min*60000. Comma or dot accepted.
Specific Gravities of Common Fluids
| Fluid |
Specific Gravity |
Notes |
| Water |
1,000 |
Reference standard |
| Hydraulic oil VG 46 |
0,870–0,880 |
Base oil and additive dependent |
| Diesel fuel |
0,820–0,850 |
Varies by blend and temperature |
| Gasoline (petrol) |
0,720–0,780 |
Lower SG → higher volatility |
| Kerosene (Jet A-1) |
0,800–0,815 |
Common aviation fuel |
| Engine oil (SAE 10W-40) |
0,860–0,890 |
Depends on formulation |
| Gear oil (SAE 80W-90) |
0,880–0,910 |
Higher due to additives |
| Brake fluid (DOT 4) |
1,040–1,080 |
Glycol-based |
| Coolant (ethylene glycol 50%) |
1,070–1,080 |
Water mix dependent |
| Transmission fluid (ATF) |
0,830–0,870 |
Similar to light hydraulic oil |
| Crude oil (light) |
0,790–0,850 |
Highly variable |
| Seawater |
1,025 |
Salinity ≈ 35 ppt |
| Milk |
1,028–1,035 |
Slightly denser than water |
| Mercury |
13,534 |
Very dense metal |
Approximate Orifice Coefficients
L = orifice length, D = orifice diameter, r = entrance radius, C = coefficent of discharge.
| Description |
L/D |
r/D |
C |
| Sharp-edged orifice (thin plate) |
0 |
0,00–0,05 |
0,61 |
| Round-edged orifice (fully rounded) |
0 |
0,15–0,25 |
0,98 |
| Short tube — separation |
0,25–0,50 |
0,00–0,05 |
0,61 |
| Short tube — no separation |
0,50–1,00 |
0,05–0,10 |
0,80 |
| Short tube with rounded entrance |
0,50–1,00 |
0,15–0,25 |
0,97 |
| Reentrant (Borda) tube, length < 0,5D |
<0,50 |
0 |
0,54 |
| Reentrant tube, length 2–3D |
2,00–3,00 |
0 |
0,72 |
| Borda mouthpiece (classic reentrant) |
≈1,00 |
0 |
0,51 |
| Smooth, well‑tapered nozzle |
2,00–5,00 |
— |
0,98 |