How many concrete blocks for a 20 ft long, 4 ft high wall?

A 20 ft long, 4 ft high wall (80 sq ft) needs 90 standard 8×8×16 blocks — buy 95 with 5% extra — laid in 6 courses, plus about 8 bags of 80 lb mortar mix.

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Quikrete Mortar Mix: up to 13 blocks per bag.

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Your results

8×8×16 blocks needed95
80 lb bags of mortar mix8
Wall area80 sq ft
Courses (rows) high6
How many concrete blocks for a 20 ft long, 4 ft high wall — diagram

Breakdown

  • Blocks per course: 15 (each block covers 16 in of length)
  • Courses: 6 (8 in each)
  • Total: 90 blocks, 95 with waste
  • Mortar: 8 bags of 80 lb mix

Need cores filled? Grout and rebar quantities depend on the engineering of the wall; retaining and foundation walls need a design that meets local code.

The math

20 × 4 = 80 sq ft × 1.125 = 90 blocks × 1.05 waste = 95 blocks · ÷ 13 per bag = 8 bags

Common questions

How many blocks for a 20x4 wall?

90 standard 8×8×16 blocks, or 95 with 5% waste.

Want the full method, tips and other sizes? See the concrete block calculator guide.

Last reviewed November 1, 2026. Results are estimates — confirm with your supplier.

Similar sizes

16 × 4 ft wall24 × 4 ft wall32 × 4 ft wall40 × 6 ft wall50 × 6 ft wall

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