How Many Blocks for a Garden Wall?
A 20×4 ft garden wall is 80 sq ft — 90 blocks at 0.889 sq ft per face, 95 with waste, plus 3 bags of mortar. Fully grouted, it drinks 0.7 yards of grout. This guide counts units, mortar, and grout in one pass, plus footing and drainage details that keep walls standing.
Step-by-Step Takeoff
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1
Check frost depth and dig the footing below it; add a 4-in drain tile behind retaining walls.
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2
Blocks: 80 ÷ 0.889 = 90 → 95 with 5% waste.
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3
Mortar: 95 ÷ 35 = 3 bags (80 lb).
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4
Grout (full): 95 × 0.2 ÷ 27 = 0.7 cu yd.
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5
Drop vertical rebar every 32 in from footing to top course before grouting.
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6
Backfill in lifts with gravel, not soil, against the back face.
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7
Set grout level and prices in the Block Wall Calculator.
Guide FAQ
Do garden walls need grout?
Low dry-stack garden walls often need none; retaining and tall walls need partial or full grout with rebar.
How much mortar per block?
About one 80 lb bag per 30–40 blocks at 3/8-in joints.
How deep a footing for a 4 ft wall?
Below frost line, typically 12 in deep by 24 in wide for garden walls — deeper for retaining.
Do I need drainage behind the wall?
Yes for any retaining wall: 4-in perforated pipe in gravel at the footing plus weep holes.
Dry-stack or mortared?
Dry-stack to 2 ft for planting beds; mortared (or surface-bonded) above that or anywhere structural.
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