Floor Mud & Mortar Bed Calculator
Calculate the exact amount of floor mud (dry-pack mortar) needed for shower floors, flat bathroom floors, and pre-slope layers. Supports site-mixed Portland cement mortar (1:5 and 1:4 ratios per ANSI A108.1A) and popular pre-mixed products including Quikrete Floor Mud, Quikrete Deck Mud, Sakrete Sand Mix, Custom FloorMud, and Laticrete 226 Thick Bed. Uses the geometrically correct center-drain volume formula — not the commonly-used simple average that underestimates by up to 25%.
Application Type
ANSI A108.1A §2.3.6 — minimum 1½” mortar bed for shower receptors. Use 1:4 cement:sand mix per ANSI A108.1A §2.3.
Drain Configuration
Uses V = L × W × [d_drain + slope × (L+W)/6] — the geometrically correct 4-plane formula. The commonly-used simple average underestimates by up to 25% of the slope component.
Floor Dimensions
Depth & Slope
Mix Type
Standard floor ratio per ANSI A108.1A §2.2.1 · 19 lb cement + 102 lb sand per cu ft placed.
Pre-Slope Layer (Optional)
Waste Factor
Recommended Tools & Materials
Affiliate Disclosure: As an Amazon Associate, we earn from qualifying purchases. We may earn a commission if you purchase through our links, at no additional cost to you. We only recommend products relevant to this project.
Quikrete Floor Mud 80 lb (#1548-81)
$13–$17
Pre-blended Portland cement and graded sand for thick mortar beds. Highest yield among mainstream products at 0.66 cu ft per 80 lb bag. 28-day strength >5,000 psi. ANSI A108.1A compliant.
Check Price on Amazon#ad · paid link
Portland Cement Type I/II — 94 lb bag
$14–$18
Required for site-mixed mortar beds (1:4 or 1:5 ratio). One 94 lb bag yields approximately 4.9 cu ft of placed mortar at 1:5, or 4.1 cu ft at 1:4. ASTM C150 Type I/II.
Check Price on Amazon#ad · paid link
Welded Wire Mesh 2"×2" 16-Gauge Galvanized — 5 ft × 50 ft Roll
$65–$85
ANSI A108.02 §3.7.3 specifies 2"×2" 16-gauge galvanized WWR placed at mid-depth of mortar beds. Required for unbonded flat beds (TCNA F111) and shower pans over 65 sq ft. Recommended for all shower mortar beds.
Check Price on Amazon#ad · paid link
Magnesium Float — 16" × 3¼" with Wood Handle
$18–$25
Essential for screeding and finishing dry-pack mortar beds. Magnesium provides a smooth drag with good bite for initial leveling. Use with a straightedge to establish proper slope.
Check Price on Amazon#ad · paid link
Stanley FATMAX 25 ft. Classic Tape Measure (33-725)
$20–$26
Industry-standard 25ft tape measure with BladeArmor coating, 14ft standout, and 16"/19.2" stud center markings in a cushion-grip high-impact case.
Check Price on Amazon#ad · paid link
Empire e70.48 True Blue 48-Inch Professional Aluminum Box Level
$30–$40
Professional-grade 48-inch level with 6061 aircraft aluminum, ±0.0005"/inch accuracy, permanently armored Lucite vials, shock-absorbing end caps, and oversized hand holes.
Check Price on Amazon#ad · paid link
Industry Standards Referenced
ANSI A108.1A
TCNA B415
TCNA B421
TCNA F111
TCNA F112
TCNA F145
IPC 417.5.2
ANSI A108.02 §3.7.3
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Related Calculators
Backsplash Tile Calculator
Calculate exactly how many tiles, bags of grout, thinset, and trim pieces you need for your kitchen backsplash. Covers ceramic, porcelain, glass, marble, mosaic, and more. Uses TCNA/ANSI formulas.
Concrete Calculator
Enter your dimensions and instantly get cubic yards, 80lb bag count, and ready-mix volume. Covers slabs, footings, columns & stairs. Includes waste factor.
Flooring Calculator
How many boxes of flooring do you need? Enter your room size and get exact boxes with waste factored in. Covers tile, hardwood, laminate, LVP, and carpet.
How to Use This Calculator
- Select application type: Choose finish shower bed, pre-slope layer (under liner), or flat floor bed. Each type applies different ANSI/TCNA requirements.
- Select drain type: Center drain (4-plane slope), linear drain (single-plane), or no drain (flat/countertop). Drain type changes the volume formula.
- Enter dimensions: Length and width in feet and inches.
- Set depth at drain and slope rate: Default 1¼" at drain and ¼"/ft slope. ANSI A108.1A requires a 1½" minimum finished shower bed.
- Choose mix type: Site-mixed 1:5 (standard floor) or 1:4 (shower/richer), or select a pre-mixed bagged product.
- Add pre-slope layer (optional): For clamping ring drains, check the box to calculate the pre-slope layer under the liner separately.
- Adjust waste factor: 10% default. 5% for simple flat beds, 15% for complex or first-time installs.
- Click Calculate: See volume, bags or cement/sand quantities, wire mesh area, and depth verification.
Why the Center-Drain Formula Matters
A center drain divides the shower floor into 4 triangular sloped planes converging at the center. The correct volume formula is V = L × W × [d_drain + slope × (L+W)/6]. The commonly suggested simple average — (d_drain + d_perimeter)/2 — underestimates the slope component by 25% for center drains, growing larger with bigger showers and steeper slopes. On a 4×4 ft shower with ¼"/ft slope, this difference is about 0.11 cu ft — enough to run short mid-pour.
Frequently Asked Questions
What is the correct mix ratio for shower floor mortar?
ANSI A108.1A §2.3 specifies a 1:4 Portland cement-to-sand ratio (by volume) for shower receptor mortar beds — a richer mix than standard floor beds. For flat floor beds, ANSI A108.1A §2.2.1 specifies 1:5. The NTCA confirms that ratios outside the 1:4 to 1:6 range are problematic: 1:3 is too rich (brittle, crack-prone) and 1:6 is too lean (low strength, unstable).
Why does the center-drain formula matter?
A center drain creates 4 triangular sloped planes — not a simple wedge. The correct volume formula is V = L × W × [d_drain + slope_rate × (L+W)/6]. The commonly-used simple average method — (d_drain + d_perimeter)/2 — underestimates the slope component by 25%. On a 4×4 ft shower with 1" at drain and ¼"/ft slope, the simple average gives 1.667 cu ft while the correct formula gives 1.778 cu ft (6.3% underestimate). This error grows with larger showers and steeper slopes — enough to run short mid-pour.
Do I need a pre-slope layer for my shower?
Yes, if your installation uses a clamping ring drain (traditional PVC/CPE liner method). Every TCNA shower method with a clamping ring drain (B414, B415, B420) requires a pre-slope under the liner that slopes at ¼"/ft minimum to the drain weep holes. The pre-slope is NOT required when using topical bonded waterproofing systems (TCNA B421/B422) such as Schluter KERDI, Laticrete Hydroban, or USG Durock — those systems slope the mortar bed itself and apply the membrane on top.
What is the minimum mortar bed thickness for a shower?
ANSI A108.1A §2.3.6 requires a 1½" minimum mortar bed for shower receptors. Some TCNA-referencing sources and Custom Building Products drawing CB415a show 1" minimum, but the ANSI standard is normative. The conservative position is 1½". For flat floor beds: TCNA F112 (bonded on concrete) requires ¾" minimum; TCNA F111 (unbonded on concrete) requires 1¼" minimum; TCNA F145 (over wood subfloor) also requires ¾" minimum with metal lath.
How many bags of Quikrete Floor Mud do I need?
Quikrete Floor Mud #1548 yields 0.66 cubic feet per 80 lb bag and 0.50 cubic feet per 60 lb bag, per the Quikrete April 2024 TDS. Divide your total mortar volume (after adding 10% waste) by the yield to get bags, then round up. For example: 3.5 cu ft needed with 10% waste = 3.85 cu ft ÷ 0.66 = 5.83 → 6 bags of 80 lb Floor Mud. This is the highest-yield mainstream floor mud product available.
Does wire mesh reinforcement go in the middle of the mortar bed?
Yes. Per ANSI A108.02 §3.7.3, 2"×2" 16-gauge galvanized welded wire reinforcement (WWR) must be placed at mid-depth — not at the bottom or top. Install half the mortar, lay the mesh flat without touching walls or curbs, then pack the remaining mortar on top. WWR is required for unbonded flat mortar beds per TCNA F111, and for shower pans over 65 sq ft per ANSI A108.1A-2017. It is recommended for all shower mortar beds regardless of size.