Capacity, span, lift height, duty class and trolley type โ the five numbers that decide whether a double girder crane is the right tool for heavy industry or an expensive mistake. Written for buyers who need a specification, not a sales pitch.
A double girder crane is the right choice for heavy lifting jobs from 20 to 100+ tons, spans beyond 22 meters, and operations that run two shifts a day: the twin box girder design carries bending loads far more efficiently than a single girder, which is why steel mills, shipyards and power plants almost always pick it. But it costs 20-30% more than a single girder crane at the same capacity, so you only want it when the job actually demands it. Capacity, span, lift height and duty class are the four numbers that determine both price and lifespan, and each one follows a simple rule: start from your heaviest regular load, measure your real building dimensions, and match the duty class to actual hours of use. This guide walks through each decision with typical ranges โ 10-100+ tons capacity, 10.5-35 m span, 8-22 m lift height, A5-A8 duty classes โ and closes with a specification template you can send to any supplier for an accurate quote.
Capacity is where most buyers either overspend or under-spec. The temptation is to buy "a bit bigger in case we need it later." The reality: every ton of extra capacity adds steel, price, and a heavier runway โ and a crane that never lifts near its rating is still charged for its rating.
Start with the heaviest single item you move on a regular basis. Not the one-off job you did three years ago โ the regular one. Then apply the standard margin: sizing to at least 125% of that load covers the load test requirement and leaves room for fixtures, slings and spreader beams. A crane rated for 32 tons that routinely lifts 28-ton coils is working near its test limit; that is a duty-cycle problem waiting to happen.
| Capacity | Typical regular loads | Where it fits |
|---|---|---|
| 10 - 16 t | Machine tools, molds, subassemblies to 13 t | Heavy machine shops, fabrication, maintenance bays |
| 20 - 32 t | Steel coils, castings, large pumps to 26 t | Steel service centers, metal fabrication, pre-cast yards |
| 50 t | Heavy equipment, transformer parts, sections to 40 t | Steel mills, power plants, shipyard fabrication halls |
| 75 - 100+ t | Turbine components, ladles, huge fabrications to 80+ t | Power plants, heavy equipment assembly, port workshops |
One more thing worth saying: if your heaviest regular load sits below 16 tons and your span is under 22 meters, a single girder crane is usually the cheaper answer โ you can read our single girder crane sizing guide for those numbers. Double girder cranes earn their keep in the 20-100+ ton zone and on wide spans, and that is exactly where the twin girder design pays for itself.
Span is the distance between the runway rails, measured center to center. It should match your building columns โ not the building width, not the bay size. Measure the existing runway rail spacing if you have one, or the column center distance for a new building, and specify that number in millimeters so there is no ambiguity with the manufacturer.
Double girder cranes typically cover spans from 10.5 to 35 meters, with heavy-duty designs reaching 40+ meters on special projects. The twin box girders carry bending loads much more efficiently than a single girder, which is why double girder is the standard choice above 22 meters or above 20 tons. Deflection is normally controlled to span/800 for cranes with an electric hoist and span/1000 for cranes with a dedicated trolley โ that stiffness is what lets a 50-ton crane position a load within a few millimeters.
Lift height is the vertical distance from the floor to the crane hook at its highest position. Most facilities need 8-14 meters, but tall fabrication halls with gantry-style work areas go to 18-22 meters. The rule: measure from the floor to the underside of your runway beam, subtract the crane dimensions plus hook path clearance, and round down. More lift height means more hoist rope, a taller trolley, and higher cost โ so specify what you actually need, not "as high as possible."
Duty class is the most commonly mis-specified number on a crane order. It is not about capacity โ it is about how many hours per day the crane works, how often it lifts near its rated load, and how many cycles it completes per hour. Pick too low a class and the crane fatigues early; pick too high and you pay for steel you never load.
| Duty class | Working hours / day | Typical applications |
|---|---|---|
| A5 | 5 - 8 hours | General fabrication, machine shops, warehouses |
| A6 | 8 - 16 hours | Steel mills, pre-cast yards, heavy fabrication |
| A7 | 16 - 24 hours, heavy loads | Steelmaking, scrap handling, continuous process lines |
| A8 | 24 hours, severe duty | Ports, continuous casting plants, power plants |
A good way to think about it: a fabrication shop that runs one shift with regular lifts is an A5 application. A steel service center running two shifts feeding shears and presses is A6. A melt shop that never stops is A7 or A8. If you are not sure, count your actual crane hours for a week โ the number you get is more reliable than any guess. For maintenance cost planning by duty class, see our double girder crane maintenance & overhaul guide.
The decision is not about brand preference โ it is about the load, the span and the hours. Here is the honest comparison:
| Factor | Single girder | Double girder |
|---|---|---|
| Capacity | 1 - 20 t typical | 5 - 100+ t |
| Span | Up to 31.5 m, economical under 22 m | 10.5 - 35 m standard, 40+ m special |
| Duty class | A3 - A5 | A5 - A8 |
| Trolley | Electric hoist (chain or wire rope) | Dedicated trolley, optional auxiliary hoist, rotating grab |
| Equipment price | USD 4,200 - 48,000 FOB | USD 22,000 - 280,000 FOB |
| Headroom needed | Lower โ hoist sits close to girder | Higher โ trolley runs between girders |
The simple rule: if you need more than 20 tons, more than 22 meters of span, or more than 8 hours of operation per day with heavy lifts, go double girder. If your loads are light and your building is tight on headroom, single girder saves you 20-30% upfront. For the full cost picture of both options, our double girder crane cost & total cost of ownership guide compares equipment, installation, maintenance and energy over a 10-year horizon.
Prices below are 2026 FOB estimates for Chinese CE-certified double girder cranes with standard trolley, controls and electrification. They exclude runway steel, freight, installation and commissioning โ expect total installed cost to run roughly 50-100% above the equipment price on heavy industrial sites, because the runway, cabling and site work are bigger jobs than for a single girder crane.
| Configuration | Equipment price (FOB) | Typical installed total |
|---|---|---|
| 10 t, 20 m span, A5 | USD 22,000 - 35,000 | USD 40,000 - 65,000 |
| 20 t, 22 m span, A5-A6 | USD 38,000 - 55,000 | USD 68,000 - 95,000 |
| 32 t, 25 m span, A6 | USD 55,000 - 85,000 | USD 100,000 - 150,000 |
| 50 t, 25 m span, A6-A7 | USD 75,000 - 130,000 | USD 140,000 - 230,000 |
| 75 t, 28 m span, A7 | USD 110,000 - 180,000 | USD 200,000 - 320,000 |
| 100 t, 30 m span, A7-A8 | USD 150,000 - 280,000 | USD 275,000 - 500,000 |
Two notes on comparing quotes. First, make sure every supplier quotes the same duty class โ a 50-ton A7 crane costs noticeably more than a 50-ton A5 crane, and comparing the two as if they were the same machine will mislead you. Second, ask what is included: some prices cover the crane only, others include runway steel, festoon cabling and installation. Our double girder crane for steel mills guide shows how these specifications play out in a real heavy-industry setting.
A vague enquiry gets a vague quote. A complete specification gets comparable quotes โ and saves you from paying for a "change order" later. Send every supplier the same ten items:
Include a simple site drawing if you can โ building cross-section with runway level, column spacing and floor layout. It costs nothing to attach and it removes more guesswork than any written description.
Start from your heaviest regular single load, multiply by at least 1.25 to cover the load test margin, and round up to a standard capacity. 10-16 tons covers heavy machine shops, 20-32 tons steel service centers, 50 tons steel mills and power plants, 75-100+ tons heavy equipment assembly. Never buy exactly at your load โ you lose the test margin and the crane fatigues faster.
Standard double girder cranes cover spans from 10.5 to 35 meters, with heavy-duty designs reaching 40+ meters. Above 22 meters the twin box girder design is normally the better choice because it carries bending loads more efficiently than a single girder. Deflection is held to span/800 with an electric hoist and span/1000 with a dedicated trolley.
A5 for 5-8 hours of regular medium work, A6 for 8-16 hours (steel mills, pre-cast yards), A7 for 16-24 hours with heavy loads (steelmaking, scrap handling), A8 for continuous severe duty (ports, casting plants). If you run two shifts with heavy lifts, A6 is normally the minimum.
When capacity exceeds 20 tons, span exceeds 22 meters, you need a dedicated trolley with auxiliary hoist or rotating grab, or the duty class is A6 or higher. Double girder cranes cost 20-30% more but handle heavier loads, wider spans, higher duty and faster travel. For light loads under 16 tons on short spans, a single girder crane is usually more economical.
Equipment prices run USD 22,000-280,000 FOB for 10-100 ton cranes with 20-30 m spans. A 10-ton, 20 m span unit is about USD 22,000-35,000; a 50-ton, 25 m span unit about USD 75,000-130,000; a 100-ton, 30 m span unit about USD 150,000-280,000. Installed totals add roughly 50-100% for runway steel, installation, electrical work and commissioning on heavy industrial sites.
Send us your bay dimensions, heaviest load and operating hours โ our engineering team will confirm the right capacity, span and duty class before you commit to anything. Quotes include a full specification sheet you can compare with other suppliers.
Request a Quote View Double Girder Crane ProductsRelated articles:
Double Girder Crane Cost & Total Cost of Ownership Guide (2026)
Double Girder Crane Maintenance & Overhaul Guide: Schedules, Costs & Best Practices (2026)
Double Girder Crane for Steel Mills: Installation Guide, Sizing & Cost
How to Size a Single Girder Crane: Capacity, Span, Lift Height & Duty Class Selection Guide (2026)
Double Girder Crane Guide: Types, Specs & Applications (2026)