Intersections = bars one way × bars the other way. A 6 × 4 m grid of 12 mm bars at 200 mm with 50 mm cover has 20 × 30 = 600 crossings; tying every other one needs 300 ties and about 1.4 kg of 1.6 mm wire. The grid weighs 209 kg (8.7 kg/m²).
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Ties = 600 × 0.5 = 300; wire = 300 × 300 mm of 1.6 mm wire = 1.4 kg
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Formulas
Bars each way = ⌊(span − 2 × cover) ÷ spacing⌋ + 1Intersections = bars along length × bars along widthTies = intersections × fraction tiedTie wire = ties × length per tie × π/4 × 1.6² mm² × 7,850 kg/m³
Worked example
A 6 × 4 m grid, 12 mm bars at 200 mm both ways, 50 mm cover, alternate crossings tied with 300 mm of wire:
Bars = 20 along the length × 30 along the width
Intersections = 600 → ties = 300
Tie wire = 300 × 4.7 g = 1.4 kg
Grid steel = 208.6 kg = 8.69 kg/m²
Crossings per m² by spacing (both ways)
Spacing
Crossings per m²
Ties (alternate)
150 mm
44.4
22
200 mm
25.0
13
250 mm
16.0
8
300 mm
11.1
6
Frequently Asked Questions
How many ties does a rebar grid need?
Count the intersections (bars one way × bars the other way). Many specifications allow tying alternate intersections in the field and every intersection around the edges; heavy mats or walkable mesh may need every crossing tied.
How much tie wire do I need?
About 250–350 mm of 1.6 mm (16 gauge) annealed wire per tie (roughly 5 g). 1,000 ties use about 5 kg.
How many ties per square metre?
At 200 mm spacing both ways there are 25 crossings per m², about 12–13 ties if alternate crossings are tied.
