Nm3/hr to M3/hr .

Normal conditions are defined as 0°C (273K) and 1 atm absolute.

So if actual m³/h = Q_act, normal m³/h = Q_N, actual temp and absolute pressure are P_act , atm and T_act , K

Q_act = Q_N x T_act /(273 x P_act)

Codey

Sorry to add more...

From universal gas law for ideal gas,

PV = (m/MW) RT [Eq.1]

P = the absolute pressure of the gas, in Pa
m = mass, in kg
MW = molecular weight, in kg-mole
V = the volume of the gas, in m3
T = the absolute temperature of the gas, in K
R = the universal gas law constant of 8.3145 m3·Pa/(mol·K)

To relate it to real gas condition, compressibility factor (z) is added.

PV = z (m/MW) RT.[Eq.2]

At condition 1 ==> P₁ x V₁ = z₁ (m₁ / MW₁) R x T₁ [Eq.3]
At condition 2 ==> P₂ x V₂ = z₂ (m₂ / MW₂) R x T₁₂ [Eq.4]

Same gas composition and flow or quantity
==> MW₁=MW₂, m₁=m₂,

[Eq.4] / [Eq.3]
==> (P₂/P₁) x (V₂/V₁) = (z₂/z₁) x (T₂/T₁)
==> V₂ = (z₂/z₁) x (T₂/T₁) x (P₁/P₂) x V₁

Using Volumetric rate (Q),
==> Q₂ = (z₂/z₁) x (T₂/T₁) x (P₁/P₂) x Q₁

If condition 2 is actual (act) and condition 1 is normal(N) (i.e. 1 atm @ 0 degC)

At Normal condition Z₁=Z_n~1, P₁ = P_act = 1 atm
==> Q_act = z₂ x Q_N x T_act / (273.15 x P_act)
where P_act in atm,

Above equation same as equation presented by Codemaster in post #1 but with inclusion of compressibility factor to relate ideal to real gas condition,The z2 factor could be range from 0.5 to 1.2 subject to composition, pressure and temperature. At low pressure, z could be closed to 1. This end-up with Codmaster equation.

The relationship between ideal and real can be more complicated as derived in by Van der Waals, Redlick-Kwong, Peng-Robinson, etc. Read more in http://en.wikipedia.org/wiki/Real_gas