SIMPLE, mulitply the Groundspeed by the required 'gradient' equals the rate of climb..EG.154knots(gross weight A320)x2.4%=400'rate o'climb..
or 2,4% 0f 6070(feet per Knot)x120knots=145'per nuatical mile x 120(2nautical miles /minute)=291'rate'o'climb..
Cheers
