Conveyor Capacity, Belt Speed and Length Calculator

Volume and mass flow on a troughed belt, with belt speed from the drive pulley and the length of the belt

Inputs

Belt width (mm)Nominal belt width, for example 1200 for a 1200mm belt.Belt speed (m/s)Design belt speed. Higher speeds lift capacity but also wear and dust.Bulk density (t/m³)Loose bulk density of the material, not solid density. Coal is roughly 0.8, iron ore 2.2 to 2.6.Trough angle (degrees)Idler trough angle. Three-roll troughs are commonly 20, 35 or 45 degrees.Surcharge angle (degrees)The angle the material heaps at on a moving belt, typically 5 to 10 degrees below the angle of repose.Fill factor (%)Allowance for uneven loading and surge. Design is commonly rated at 70 to 95 per cent of theoretical.

Belt speed and length

Optional. Work out the belt speed from the drive pulley, and the belt length for a two-pulley conveyor.

Drive pulley diameter (mm)Outside diameter including lagging.Drive pulley speed (rpm)Centre distance (m)Head pulley centre to tail pulley centre.Tail pulley diameter (mm)

Mass flow

2,223t/h

At 90% fill factor

Volume flow

1,389m³/h

Cross-sectional area

0.1715m²

Usable belt width 1030mm

Load per metre

247.0kg/m

Material carried per metre of belt, useful for a first look at tension and idler loading.

Belt speed from the drive pulley

2.51m/s

Matches the belt speed entered above

Belt length (endless)

302.5m

Open two-pulley belt, before any allowance for take-up travel and splices.

How it's calculated

Belt and material

Width, trough, surcharge

Cross-sectional area

Trough + surcharge cap

Capacity

3600 × A × v × ρ

Mass flow = 3600 × A × v × ρ, where A is the cross-sectional area of material on the belt in m², v is belt speed in m/s and ρ is bulk density in t/m³.

Cross-sectional area is the troughed trapezoid plus the surcharge cap above it. Usable width is taken as 0.9B − 0.05 m for belts up to 2m, which leaves the standard edge margin. The trough area uses three equal idler segments, and the surcharge is treated as a proper circular segment rather than a triangle, which a triangular approximation overstates by roughly half.

The fill factor then discounts the theoretical figure for uneven loading, surge and feed variation.

Belt speed = π × D × n ÷ 60, where D is the drive pulley diameter in metres and n its speed in rpm.

Belt length = 2C + π(D₁ + D₂) ÷ 2 + (D₂ − D₁)² ÷ 4C for an open belt around two pulleys of diameters D₁ and D₂ at centre distance C. Add the take-up travel and a splice allowance for an order length.

This is a concept sizing estimate. Detailed design accounts for incline, idler geometry, material lump size, tension, drive power and takeup, and is normally done against CEMA or ISO 5048 or your own engineering standards.

How to calculate conveyor capacity: a worked example

Take the belt the calculator opens with: 1200 mm wide, running at 2.5 m/s, on 35 degree three-roll idlers, carrying a material with a loose bulk density of 1.6 t/m³ that heaps at a 20 degree surcharge angle, with a 90 per cent fill factor for uneven loading.

Step	Calculation	Result
Usable width	0.9 × 1.2 m − 0.05 m	1.03 m
Cross-sectional area	Troughed trapezoid plus the surcharge cap	0.1715 m²
Volume flow	3600 × 0.1715 × 2.5 × 0.9	1,389 m³/h
Mass flow	1,389 × 1.6	2,223 t/h
Load per metre	2,223 × 1000 ÷ (2.5 × 3600)	247 kg/m

Quote the loose bulk density, not the solid density. Iron ore is about 2.4 t/m³ loose and over 4 solid, and the wrong one overstates the belt by more than half.

Belt speed and belt length

Belt speed follows from the drive pulley: speed = π × D × n ÷ 60, with D the pulley diameter in metres and n its speed in revolutions per minute. An 800 mm pulley at 60 rpm gives π × 0.8 × 60 ÷ 60 = 2.51 m/s, which is the figure to check against the speed assumed in the capacity calculation. A gearbox ratio change or a variable speed drive shows up here first.

The endless length of an open belt around two pulleys is 2C + π(D₁ + D₂) ÷ 2 + (D₂ − D₁)² ÷ 4C, where C is the centre distance. With 800 mm head and tail pulleys 150 m apart that is 2 × 150 + π × 0.8 = 302.5 m. For an order, add the take-up travel, the splice allowance the belt supplier specifies, and the extra for any snub, bend or gravity take-up pulleys the belt wraps.

Quantity	Formula	Example
Belt speed	π × D × n ÷ 60	π × 0.8 × 60 ÷ 60 = 2.51 m/s
Belt length, equal pulleys	2C + π × D	2 × 150 + π × 0.8 = 302.5 m
Belt length, unequal pulleys	2C + π(D₁ + D₂) ÷ 2 + (D₂ − D₁)² ÷ 4C	Adds a small term for the difference

Getting the inputs right

Surcharge angle is material behaviour, not a constant. It is commonly 5 to 10 degrees below the angle of repose and falls as material gets wetter or is loaded off-centre. Run the range, not the design point.
Fill factor is where surge and feed variation live. A plant fed by trucks or a reclaimer sees peaks that a 100 per cent fill factor pretends do not exist.
Belt speed above about 3.5 m/s moves transfer and skirt design to the front of the problem, and above 5 m/s dust, wear and tracking need particular care.
This is concept sizing. Detailed design to CEMA, ISO 5048 or the owner's standard adds incline, idler geometry, lump size, tension, power and take-up, and is where the design brief has to be right.

Why it matters

Conveyor capacity is where a lot of bulk handling problems start. Size a belt on optimistic assumptions and every downstream chute, crusher and stockpile inherits the error. Size it on the design point alone and it will struggle the first time the material comes through wetter, finer or faster than the specification said it would.

The two inputs that catch people out are bulk density and surcharge angle. Density is often quoted as solid density rather than loose bulk density, which overstates tonnes on the belt. Surcharge angle is material behaviour, not a constant, and it drops as material gets wetter or is loaded off-centre. Running the numbers across the real range, rather than at one design point, tells you whether the belt has genuine headroom or only has it on paper.

Common questions

How do you calculate conveyor capacity?

Capacity in t/h = 3600 × A × v × ρ, where A is the cross-sectional area of material on the belt in m², v is belt speed in m/s and ρ is loose bulk density in t/m³. The area comes from the belt width, trough angle and surcharge angle, and a fill factor discounts it for uneven loading. The calculator on this page does the geometry.

How do you calculate conveyor belt speed?

Belt speed = π × pulley diameter × pulley rpm ÷ 60, with the diameter in metres. An 800 mm drive pulley turning at 60 rpm moves the belt at 2.51 m/s. Use the diameter over the lagging, and the pulley speed after the gearbox.

How do you calculate conveyor belt length?

For an open belt around two pulleys, length = 2 × centre distance + π × (D₁ + D₂) ÷ 2 + (D₂ − D₁)² ÷ (4 × centre distance). With equal pulleys the last term is zero. Add take-up travel and the splice allowance before ordering.

What is surcharge angle?

The angle the top surface of the material makes with the horizontal once it has settled on a moving belt. It is lower than the static angle of repose, typically by 5 to 10 degrees, and it falls as the material gets wetter. It sets the height of the load above the trough and so a large part of the capacity.

What belt speed should a conveyor run at?

Most troughed belts in mining run between 2 and 5 m/s. Higher speed raises capacity for a given width but also wear, dust, spillage at transfers and the demands on tracking and chute design. The right speed is a design decision balanced against the transfer points, which is why belt speed appears in the design brief rather than being chosen last.

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