How to calculate duct area in meters for bent,offset,round off square,reducer duct ?

This is a geometry question.

for the sake of quantity take off, you can do assumptions. Ex: elbows equivalent to1.5m of straight duct, Tee equivalent to2.5m of straight duct...

 ABRAR AFRIDI

SPECIFICATIONS AND FORMULAS

SPECIFICATION

WIDTH

HEIGHT

LENGTH

RADIUS

DEGREE

QTY

OFFSET

FORMULAS

STRAIGHT FORMULA:

(WIDTH + HEIGHT) X 2 X LENGTH x QTY = AREA

ELBOW FORMULA:

(WIDTH + HEIGHT) X 2 X LENGTH X QTY = AREA

LENGTH = (R+W/2) X 3.14 X (DEGREE/180)

TAPER FORMULA:

(WIDTH 1 + HEIGHT 1+WIDTH 2+ HEIGHT 2) X LENGTH x QTY = AREA

IF UP/DOWN TAPER FORMULA:

(WIDTH 1 + HEIGHT 1+WIDTH 2+ HEIGHT 2) X (LENGTH + OFFSET) x QTY = AREA

OFFSET FORMULA:

(WIDTH + HEIGHT) X 2 X (LENGTH + OFFSET) x QTY = AREA

SHOE FORMULA:

(WIDTH + HEIGHT) X 2 X (LENGTH + 50 MM) x QTY = AREA

DUMMY:

WIDTH X HEIGHT = AREA

YEE PIECE FORMULA:

STRAIGHT AREA + ELBOW AREA = AREA

TEE PIECE FORMULA:

ELBOW AREA + ELBOW AREA = AREA 

NOTE: IF ALL DIMENSIONS ARE IN MM, AREA IN SQ.MM

Calculating Area of Bend required to following calculation

2 x ((Area of Circle based on duct Width +150mm as Radius /4)-(Area of circle based on 150mm as Radius/4))+Height of duct x (2 xPi()x (Duct width+150mm)/4)+(height of Duct x 2x Pi()x 150mm/4)

Calculating Reducer required Trapezium calculation 

the exact area in educational field is OK to calculate but in professional it is not like this

Normally it is given by some factor added in the duct length

Anyhow if you very keen to do so you can make a model in auto CAD and fine area of different sizes by area command

Hope this will work

another option is to measure the weight and than divide by the gauge number

means if you bend is 15 kilo and you know the gauge of elbow or bend than by this info how many kilos in that gauge you can find the almost exact area

any QS can answer this question for certifying the payment application ? exact area to be calculated for billing purposes.

when the quantity take of is complete take ten % extra of duct this will resolve the quantity assumption .

Very useful for Fresher and experienced Engineer also