Formulas and worked examples

Concrete Calculator

Concrete calculator for slabs: enter length, width, thickness in inches to get bags needed and cost. 10x10 slab, 4 in thick, needs 62 bags.

Formula cu ft = length ft x width ft x (thickness in / 12); bags = ceil(cu ft x waste / bag yield).

Example 10 ft x 10 ft x 4 in = 33.3 cu ft (1.23 cu yd); 62 x 80 lb bags; about $401.14.

Concrete Bags Calculator

Concrete bags calculator: enter length, width, thickness for 60 lb and 80 lb bag counts, waste factor, cubic yards, cost from one retailer's listing.

Formula bags = ceil(volume cu ft x waste / yield), for 60 lb and 80 lb yields above.

Concrete Footing Calculator

Calculate concrete bags for a footing trench: enter length, width, and depth to get 80 lb bag count and cost with 10% waste.

Formula cu ft = trench length ft x (width in / 12) x (depth in / 12).

Example 20 ft x 16 in x 8 in = 17.8 cu ft; 33 x 80 lb bags.

Concrete Column Calculator

Sonotube calculator for round columns and sonotube pier tubes: enter diameter and height for 80 lb bag counts, cost, and ready-mix cubic yards.

Formula cu ft = pi x (diameter in / 24)^2 x (height in / 12) x count.

Example 4 tubes, 10 in diameter, 48 in tall = 8.7 cu ft; 16 x 80 lb bags.

Concrete Steps Calculator

Concrete steps calculator and concrete stairs calculator for solid poured steps. Enter step count, riser, tread, width, landing for bag count and cost.

Formula (solid steps) cu ft = width x tread x riser x n(n+1)/2, all in feet; a landing adds width x depth x full height.

Example 4 steps, 7 in risers, 11 in treads, 48 in wide = 21.4 cu ft; 40 x 80 lb bags.

Stair Calculator

Find riser count, step height, tread run and stringer length for your staircase. For a 100 in total rise, the 7.75 in cap gives 13 equal risers.

Formula risers = ceil(total rise / 7.75); riser height = total rise / risers; treads = risers - 1; stringer = sqrt(rise^2 + run^2). The 7.75 in cap is the IRC residential riser limit.

Example 100 in total rise, 10 in treads = 13 risers at 7.69 in, 12 treads, 156 in stringers.

L-Shaped Stair Calculator

l-shaped stair calculator divides overall rise across two flights separated by a landing, giving riser counts, tread run, and landing size in inches or cm

Formula as the stair calculator, with the rise split into two flights sharing one riser height at a corner landing.

Stair Calculator with Landing

Stairs with landing calculator: split total rise into two flights sharing one riser height. Includes landing size and stringer spacing.

Formula as the stair calculator, with a mid-landing splitting the flight.

U-Shaped Stair Calculator

This u-shaped staircase calculator divides total rise between two flights that reverse at a landing. Both flights share one riser height and run parallel.

Formula as the stair calculator, with the rise split at a half landing where the stair doubles back.

Roofing Calculator

Roofing shingle calculator: get bundles, waste, and felt rolls from footprint, overhang, and pitch. 6/12 example: 50 bundles.

Formula roof area = footprint (plus overhang on each side) x sqrt(1 + (pitch/12)^2); squares = area / 100; bundles = ceil(squares x waste x 3); felt rolls = ceil(squares / 4).

Example 40 ft x 30 ft, 6/12 pitch, 1 ft overhang = 1,503 sq ft (15 squares); 50 bundles; 4 felt rolls.

Roof Pitch Calculator

Roof pitch calculator: convert a pitch like 6/12 to a slope multiplier and angle. Use the multiplier to scale footprint area to roof area.

Formula angle = atan(pitch / 12); slope % = pitch / 12 x 100; area multiplier = sqrt(1 + (pitch/12)^2); rafter length (ridge to wall line, no overhang) = span / 2 x multiplier.

Example 6/12 pitch = 26.6 degrees, 50% slope, multiplier 1.118; a 30 ft span needs 16.77 ft rafters.

Deck Calculator

Deck calculator for boards, joists and screws. Draw your deck layout, choose a board size and gap, get a materials shopping list.

Formula rows = ceil((deck width + gap) / (board face width + gap)); boards per row = ceil(deck length / board length); boards = rows x boards per row for rectangles, ceil(area / ((face width + gap) x board length)) for other shapes, cut-outs subtracted; boards with waste = ceil(boards x (1 + waste)); joists = floor(deck length / joist spacing) + 1; crossings per board = floor(board length / joist spacing) + 1; screws = 2 x boards with waste x crossings; hidden clips = boards with waste x crossings.

Defaults board face widths 5/4 x 6 = 5.5 in, 2 x 6 = 5.5 in, 2 x 4 = 3.5 in, 1 x 6 composite = 5.5 in; gap 0.125 in (5 mm metric); board lengths 8/10/12/16/20 ft (2.4/3/3.6/4.2/4.8 m); joist spacing 12/16/24 in (400/450/600 mm); waste 10%.

Example 16 ft x 12 ft, 5/4 x 6 boards (5.5 in face), 0.125 in gap, 16 ft boards, 16 in joists, 10% waste = 26 boards (29 with waste, 464 linear ft); 13 joists at 12 ft; 754 screws or 377 hidden clips.

Deck Stair Calculator

Deck stair calculator: number of risers, treads, stringers and tread boards for steps from a deck to the ground.

Formula risers = ceil(total rise / 7.75); riser height = total rise / risers; treads = risers - 1; total run = treads x tread run; stringer = sqrt(rise^2 + run^2); stringers = max(2, floor(width / 16) + 1); 2x12 stock = first of 8/10/12/14/16/20 ft at or above stringer length + 1 ft; tread boards = treads x 2 (runs up to 11.5 in) or x 3; riser boards = risers.

Example 36 in total rise, 10.5 in tread run, 36 in wide = 5 risers at 7.2 in, 4 treads, 42 in total run, 55.3 in stringers; 3 stringers from 8 ft 2x12 stock; 8 tread boards (2 per tread); 5 riser boards.

Deck Baluster Spacing Calculator

Deck baluster spacing calculator: a 6 ft railing between posts with 1.5 in balusters takes 13 at a 3.75 in gap, plus on-centre marks.

Formula n = ceil((section length - max gap) / (baluster width + max gap)), plus one if the resulting gap would reach the limit; gap = (section length - n x baluster width) / (n + 1); on-centre spacing = gap + baluster width; total = n x sections. Max gap default 4 in (100 mm), the IRC R312.1.3 sphere limit.

Example 72 in section, 1.5 in balusters, 4 in max gap = 13 balusters, 3.75 in gap, 5.25 in on centre.

Deck Footing Calculator

Deck footing calculator that gives the number of footings, concrete volume, bag count and cost from deck size, post spacing and footing size.

Formula columns = ceil(deck length / post spacing) + 1; rows = ceil(deck width / post spacing) + 1, minus one row on an attached deck (the ledger carries the house side); footings = columns x rows; cu ft = pi x (diameter in / 24)^2 x (depth in / 12) x footings; bags = ceil(cu ft x waste / bag yield).

Defaults post spacing 6/8/10 ft (1.8/2.4/3 m); footing diameter 8/10/12/16 in (200/250/300/400 mm); depth 36 in (900 mm), editable for the local frost line; attached.

Example 16 ft x 12 ft attached, 8 ft post spacing, 12 in x 36 in footings = 3 x 2 = 6 footings; 14.14 cu ft; 26 x 80 lb bags; about $168.22.

Paver Calculator

Paver calculator for patio layouts: 567 pavers for a 12x10 ft patio, with base gravel, bedding sand and joint sand estimates.

Formula pavers = ceil(area sq in / (paver width x length) x (1 + waste)); base cu ft = area sq ft x (base depth in / 12); bedding sand cu ft = area sq ft x (bedding depth in / 12); cu yd = cu ft / 27; tons = cu yd x density / 2,000 (gravel 2,835 lb per cu yd, sand 2,700); bags = ceil(cu ft / 0.5); joint sand bags = ceil(area sq ft / coverage per 50 lb bag).

Defaults paver sizes 4 x 8 in, 6 x 6 in, 6 x 9 in, 12 x 12 in, 16 x 16 in, 12 x 24 in, 24 x 24 in; pattern waste running 5%, stack 5%, herringbone 10%, diagonal 15%; base 4 in; bedding 1 in; polymeric sand coverage per 50 lb bag: 1/8 to 1/4 in joints 88 sq ft, 3/8 to 1/2 in 50 sq ft, 3/4 to 1 in 28 sq ft.

Example 12 ft x 10 ft, 4 x 8 in pavers, 5% waste = 567 pavers; base 4 in = 40 cu ft (1.48 cu yd, 2.1 tons, 80 bags); bedding sand 1 in = 10 cu ft (0.37 cu yd, 0.5 tons, 20 bags); joint sand 2 x 50 lb bags at 88 sq ft per bag.

Paver Sand Calculator

Paver sand calculator for the bedding layer and joints. Example: 12x10 ft patio uses about half a ton of bedding sand. Inches or metric.

Formula bedding sand cu ft = area sq ft x (depth in / 12); cu yd = cu ft / 27; tons = cu yd x 2,700 / 2,000; bags = ceil(cu ft / 0.5); joint sand bags = ceil(area sq ft / coverage per 50 lb bag by joint width: 88, 50 or 28 sq ft).

Example 12 ft x 10 ft at 1 in = 10 cu ft (0.37 cu yd, 0.5 tons, 20 x 0.5 cu ft bags); joint sand for 1/8 to 1/4 in joints = 2 x 50 lb bags.

Paver Base Calculator

Paver base calculator: find cubic feet, cubic yards or tons of gravel for patios and driveways, and see how many bags to buy.

Formula cu ft = area sq ft x (depth in / 12) x (1 + extra); cu yd = cu ft / 27; tons = cu yd x 2,835 / 2,000; bags = ceil(cu ft / 0.5). Default depth 4 in (patios; 6 to 8 in for driveways), extra 10%.

Example 10 ft x 10 ft at 4 in = 33.3 cu ft (1.23 cu yd, 1.75 tons); with 10% extra = 36.7 cu ft (1.36 cu yd, 1.93 tons, 74 bags).

Paving Calculator

Use this UK paving calculator to estimate paving slabs or block paving, sharp sand laying course and MOT Type 1 sub-base in tonnes and bulk bags.

Formula (metric) slabs or blocks = ceil(area m2 / (width m x length m) x (1 + waste)); sharp sand m3 = area m2 x laying course mm / 1,000; MOT Type 1 m3 = area m2 x sub-base mm / 1,000; tonnes = m3 x density (sharp sand 1.6 t per m3, MOT Type 1 2.1 t per m3 compacted); bulk bags = ceil(tonnes / 0.85).

Defaults sizes 200 x 100 mm block, 400 x 400 mm slab, 450 x 450 mm slab, 600 x 300 mm slab, 600 x 600 mm slab, 900 x 600 mm slab; laying course 40 mm for slabs, 30 mm for blocks; sub-base 100 mm (150 mm for driveways); bulk bag 0.85 t; waste 5%.

Example 4 m x 3 m, 600 x 600 mm slabs, 5% waste = 35 slabs; sharp sand at 40 mm = 0.48 m3 (0.77 t, 1 bulk bag); MOT Type 1 at 100 mm = 1.2 m3 (2.52 t, 3 bulk bags).

Square Footage Calculator

Square footage calculator and how to calculate square footage: multiply length by width. Works in feet and meters on one page.

Formula sq ft = length ft x width ft; rectangles sum for L-shapes.

Cubic Yard Calculator

Use the DIY Totals cubic yard calculator to find the cubic yards you need. Enter length, width, and depth in inches for a bulk material order estimate.

Formula cu yd = length ft x width ft x (depth in / 12) / 27.

Square Feet to Acres

Convert square feet to acres or acres to square feet. One acre equals 43,560 square feet. Use the calculator for lots, gardens, and lawns.

Formula acres = sq ft / 43,560.

Square Meters to Square Feet

Convert square meters to square feet and back. 1 sq m = 10.7639 sq ft. Use the calculator for property and material areas.

Formula sq ft = sq m x 10.7639.

Cubic Feet to Cubic Yards

Convert cubic feet to cubic yards. One cubic yard is 27 cubic feet. Check bag and truck load estimates for soil, mulch, and gravel.

Formula cu yd = cu ft / 27.

Tons to Cubic Yards

Convert tons to cubic yards for gravel, sand, topsoil, mulch, crushed stone, and fill dirt. Enter tons and choose a material to get the volume.

Formula cu yd = tons x 2,000 / density lb per cu yd.

Densities (lb per cu yd, US retail averages): Gravel 2,835, Sand 2,700, Topsoil 2,025, Mulch 675, Crushed stone 2,700, Fill dirt 2,160, Concrete 4,050.

Example 3 tons of gravel = 2.12 cu yd.

Concrete Slab Sizes

Pre-computed bag counts, cost and cubic yards for 34 common slab sizes at 4 in thick (6 in variant shown on-page), from /measurement/8x8-concrete-slab through /measurement/40x60-concrete-slab.