Rebar · TMT Bar · Reinforcement Steel · Estimating
Rebar & TMT Weight Calculator
Calculate theoretical reinforcement-bar weight from diameter, length, and quantity. Use standard global metric bar sizes or enter a custom diameter, then switch between metric and imperial results for estimating, bar-bending schedules, procurement checks, and site reconciliation.
The diagram shows the nominal cross-section and a simplified ribbed profile. Labels update as you change the diameter and length.
Fix the highlighted field above to see the rebar weight.
Engineering Reference
What Rebar Weight Really Depends On
Rebar quantity is often scheduled in pieces and lengths but purchased by mass. The theoretical result starts with nominal diameter, steel density, bar length, and piece count. Procurement control must then account for the applicable product standard, manufacturing tolerance, actual bundle mass, cutting loss, laps, anchorage, couplers, and approved bar-bending schedules.
Nominal Bar Diameter
The selected size is the nominal diameter used for theoretical mass calculations. Standard reinforcement sizes are convenient for design and scheduling, but site acceptance should follow the applicable standard and project specification rather than a visual diameter estimate alone.
Measured or Custom Diameter
Custom input is useful for non-standard stock, laboratory checks, legacy reinforcement, or preliminary comparisons. A single calliper reading does not fully describe a deformed bar because the core and ribs form a non-uniform profile. Use mass-per-length verification for acceptance.
Rebar and TMT Terminology
Rebar is the global term for reinforcing steel. TMT bar commonly refers to thermo-mechanically treated deformed reinforcement. The theoretical weight calculation is the same when nominal diameter, density, and length are the same; grade and mechanical performance are separate checks.
Standard Commercial Length
Twelve metres is a common stock length and is therefore the default. Coiled reinforcement, cut-and-bend schedules, special transport limits, and regional supply practice can change the delivered length. Always calculate from the ordered or measured length.
Density-Based Theoretical Mass
The calculator uses 7850 kg/m³. This produces a consistent theoretical mass for a circular steel section. Actual bundle mass may differ because of manufacturing tolerance, rib geometry, length tolerance, surface condition, and the mass basis permitted by the applicable standard.
Rolling Margin and Site Reconciliation
Rolling margin describes the difference between theoretical and actual mass caused by manufacturing control within permitted tolerances. It should never be treated as an automatic saving. Reconcile design quantity, theoretical mass, delivery documentation, piece count, and random bundle weight.
Calculation Method
Rebar and TMT Weight Formulas
The exact method calculates the circular cross-sectional area and multiplies it by steel density. The D² / 162 formula is a compact metric shortcut used widely for site calculations. It is close to the exact result but should be treated as a rounded rule, not a substitute for contractual mass tolerances or verified bundle weighing.
- Convert the bar diameter to metres and calculate the nominal circular area.A = π × (D ÷ 2)²
- Multiply area by the standard theoretical steel density to obtain mass per metre.Weight per metre = A × 7850
- Multiply by bar length and quantity for piece and total mass.Total weight = weight per metre × L × quantity
- Exact metrickg/m = [π ÷ 4] × (D ÷ 1000)² × 7850
- Simplified exact coefficientkg/m ≈ 0.006165 × D²
- Site rulekg/m ≈ D² ÷ 162
- Weight per piecepiece weight = unit weight × bar length
- Total weighttotal weight = piece weight × quantity
- D Nominal or custom bar diameter
- A Nominal circular cross-sectional area
- L Length of one bar
- qty Number of bars
- 7850 Steel density in kg/m³
- 162 Rounded site-rule divisor
Worked Example: 16 mm Rebar, 12 m Length, 50 Pieces
- DiameterD = 16 mm = 0.016 m
- Exact unit mass[π ÷ 4] × 0.016² × 7850 = 1.5783 kg/m
- D² / 162 rule16² ÷ 162 = 1.5802 kg/m
- One 12 m bar1.5783 × 12 = 18.9400 kg
- Fifty bars18.9400 × 50 = 947.00 kg
Exact theoretical total: approximately 947.00 kg
Use theoretical mass for estimating and reconciliation. Use the applicable product standard, approved bar-bending schedule, mill documentation, piece count, and site weighing for final procurement acceptance.
Frequently Asked Questions
Rebar and TMT Weight Questions
These answers explain the difference between theoretical mass, the D² / 162 shortcut, commercial lengths, rolling tolerance, and delivered bundle weight.
How do I calculate the weight of a rebar or TMT bar?
Use the nominal or measured bar diameter to calculate the circular steel area, multiply by the density of steel, and then multiply by bar length and quantity. In metric units, the exact theoretical weight per metre is based on pi multiplied by diameter squared, divided by four, and multiplied by 7850 kilograms per cubic metre.
Is the D² / 162 formula exact?
D² / 162 is a widely used site rule for estimating kilograms per metre when D is in millimetres. It is very close to the exact density-based result, but it is still a rounded shortcut. The exact coefficient for a smooth circular section at 7850 kilograms per cubic metre is approximately D² / 162.20.
What steel density does this calculator use?
The calculator uses 7850 kilograms per cubic metre, the standard theoretical density commonly used for carbon-steel reinforcement calculations. Actual bundle weight can differ because of manufacturing tolerance, rib geometry, rolling practice, scale, and measurement variation.
Are rebar and TMT bar the same for weight calculations?
For theoretical weight, both are calculated from nominal diameter, length, quantity, and steel density. TMT describes a thermo-mechanically treated reinforcing bar, while rebar is the broader global term for reinforcement steel. Grade and mechanical properties must still be verified separately.
Why does the delivered bundle weight differ from the calculator?
The calculator gives theoretical mass from nominal geometry. Delivered bars can vary because of permitted rolling tolerances, actual diameter, rib pattern, length tolerance, surface condition, and bundle counting. Compare the calculated quantity with the applicable product standard, purchase specification, mill documents, and random site weighing.
Is 12 metres the standard rebar length everywhere?
Twelve metres is a common commercial stock length in many markets, which is why it is the default here. Suppliers may also provide other lengths, coils, or project-specific cut lengths. Enter the actual ordered or measured length for procurement and bar-bending schedules.
Does the rib pattern change the calculated weight?
The theoretical method treats the bar as a circular section at its nominal diameter. Real deformed bars include ribs and may be rolled with a core profile that differs slightly from a perfect circle. Product standards control mass per metre and tolerances, so site acceptance should use the applicable standard and verified bundle weight.
What changes when I select imperial units?
Standard bar sizes remain identified by their global metric diameters, with inch equivalents shown for reference. Custom diameter is entered in inches, length is entered in feet, and the results are displayed in pounds per foot, pounds per piece, and total pounds.
Buying and Site-Control Checklist
How to Avoid Rebar Procurement Shortages
Shortages usually come from a mismatch between design quantity, bar-bending schedules, commercial lengths, rolling tolerance, cutting loss, and received bundle mass. Control the calculation basis before ordering and verify deliveries before reinforcement is fixed or concrete is poured.
1. Reconcile drawings with the approved bar-bending schedule
Do not order only from a total tonnage shown on an early estimate. Check bar marks, diameters, member locations, cutting lengths, bends, hooks, anchorage, laps, couplers, starter bars, chairs, and approved revisions.
Freeze the issue status used for procurement and record any later design change separately. A revised lap length or member detail can change tonnage even when the structural layout appears unchanged.
2. Treat rolling margin as a controlled tolerance
Rolling margin is the difference between theoretical and actual bar mass arising from manufacturing control within permitted limits. Bars may be slightly lighter or heavier than the theoretical schedule depending on the applicable standard and production process.
Do not assume a favourable rolling margin when pricing or ordering. Specify the governing standard, mass tolerance, acceptance method, and whether payment is based on theoretical or actual weight.
3. Verify the Mill Test Certificate
Review the Mill Test Certificate for manufacturer, heat or batch identification, bar grade, nominal size, chemical composition, yield strength, tensile strength, elongation, bend or rebend results where applicable, and reference standard.
Match certificate identification with bundle tags and delivery records. The weight calculator confirms quantity; it does not confirm yield strength, ductility, weldability, or traceability.
4. Weigh random bundles at the site
Use a calibrated weighbridge, crane scale, or another approved method to check random bundles. Compare actual mass with piece count, measured length, nominal size, theoretical unit weight, and permitted tolerance.
Complete this check before the steel is dispersed across the site. Once bars are cut, bent, mixed by heat number, or fixed in reinforcement cages, resolving a delivery shortage becomes much harder.
5. Count pieces and confirm actual bar length
A bundle tag or invoice weight does not automatically confirm the required number of usable bars. Count representative bundles and measure stock length, especially where bars are supplied in non-standard lengths or cut-and-bend form.
Record damaged ends, severe bends, corrosion loss, rejected bars, and identification problems. These may be included in delivered weight but unavailable for the planned reinforcement work.
6. Allow for cutting loss and construction sequence
Optimise cutting patterns by diameter and bar mark. Separate reusable offcuts from scrap, and do not apply one blanket waste percentage to every member. Congested detailing, short links, coupler systems, and phased pours create different loss patterns.
Maintain a live reconciliation of ordered, received, issued, fabricated, fixed, returned, and scrapped reinforcement. This identifies shortage early enough to place a supplementary order before the concrete programme is affected.
Pre-pour control routine
Confirm the latest approved drawings and bar-bending schedule, reconcile theoretical tonnage, verify bundle tags and Mill Test Certificates, count representative pieces, measure length, and weigh random bundles. Compare the result with the applicable standard and purchase specification before releasing reinforcement for critical concrete work.