Rebar Weight Takeoff & Tension Lap Splice Calculator
Multi-line weight takeoff for ordering, plus ACI 318 simplified tension development and lap splice lengths. Runs entirely offline; inputs persist in this browser via localStorage.
Use limits: Where the structural drawings include a lap splice schedule or typical details, the drawings govern — this tool is for checking a suspicious lap, answering an RFI intelligently, or sanity-checking a shop drawing, not for replacing the EOR's schedule. Lap lengths here use the ACI simplified (conservative) equations for uncoated or epoxy-coated bars in tension.
For deformed bars in tension, spacing/cover Case 1:
#6 and smaller: ℓd = (fy·ψt·ψe / (25·λ·√f′c)) · db
#7 and larger: ℓd = (fy·ψt·ψe / (20·λ·√f′c)) · db
Case 2 multiplies both by 1.5 (equivalently, denominators 50/3 and 40/3). The product ψt·ψe need not exceed 1.7, √f′c is capped at 100 psi (f′c = 10,000 psi) for development calcs, and ℓd is never taken less than 12 in.
Class B lap = 1.3 ℓd (minimum 12 in.); Class A = 1.0 ℓd. Most drawings default all tension laps to Class B unless noted, because Class A requires ≥2× steel provided over the splice and ≤50% of bars spliced at one location — conditions the field can rarely verify.
Field notes
#14 and #18 bars cannot be lap spliced — mechanical or welded splices only. The tool flags this.
Grade 80 laps run a third longer than Grade 60 — check the bar tags before assuming.
Stagger and location of splices are design decisions from the drawings; this tool only computes length.
When counting laps in a takeoff: each lap adds one lap length of bar per splice. On long walls with 60-ft stock, that adds up fast enough to matter at the order.
References
ACI 318 — Building Code Requirements for Structural Concrete, development and splice provisions (Ch. 25 in current editions). https://www.concrete.org/
CRSI, Manual of Standard Practice — bar data and placing conventions. https://www.crsi.org/