How this calculation works
Model each bar as an equivalent solid circular cylinder. Convert diameter from millimetres to metres, find its cross-sectional area, multiply by total entered length and then by the chosen density. The default density is an example steel assumption.
Mass = π(d/1000)²/4 × length × quantity × densityA worked example
At 12 mm equivalent diameter and 7,850 kg/m³, theoretical mass is about 0.887814 kg per metre. One hundred 12 m bars total about 1,065.377 kg.
Good to know
A geometric material-planning estimate from the entered measurements. Check actual product dimensions and the project layout. No structural suitability, installation specification, local requirements, labor, tax or pricing is determined. Decimal input lists allow up to 6 places and at most 100 entries/rows, each no greater than 1,000,000. Equivalent cylinders only. Rib geometry, actual manufacturing tolerances, coatings, hooks, bends, laps and cutting allowances are not added. The result is not reinforcement design or a supplier’s certified mass.
Reference: NIST: example steel material density (opens in a new tab) ↗
The diameter enters through cross-sectional area
For an equivalent round cylinder, cross-sectional area is πd²/4. Doubling diameter therefore multiplies theoretical mass per metre by four when density is unchanged. Doubling bar count or entered length doubles total modeled mass.
Diameter is entered in millimetres but must be converted to metres before multiplying by length in metres and density in kilograms per cubic metre. Missing that conversion would introduce a squared unit error.
The default 7,850 kg/m³ is an example steel density assumption. Material density and the meaning of nominal bar diameter must be appropriate to the product; this calculation does not measure either property.
Theoretical geometry is different from a supplier’s mass
The density calculator expresses the same mass-volume relationship in another direction. Here the volume is constructed from equivalent circular area and the total bar length, then multiplied by the supplied density.
Ribs, coatings, production tolerances and the applicable nominal-area convention can affect comparison with real products. For purchasing, reconcile this geometric estimate with the supplier’s stated mass basis rather than treating it as a certified value.
Entered length must already represent the bar length you want to total. No hooks, bends, laps, splices or cutting allowance are added. Choosing reinforcement diameter, spacing or anchorage is not a mass-calculation task and is not evaluated here.
A few questions, answered
Does quantity include bends or laps?
No. The tool multiplies the entered length per bar by the count. Additional developed length must be included in that input if appropriate to your separate plan.
Why is this labeled theoretical?
It uses an equivalent solid round cylinder and an assumed density, without manufacturing details or a product-specific certified mass.
Does the result determine structural adequacy?
No. Mass alone does not determine reinforcement suitability, detailing or load capacity.